diff --git a/dat/Arc-goal.lua b/dat/Arc-goal.lua
index ba3a00555..8cdf65e8c 100644
--- a/dat/Arc-goal.lua
+++ b/dat/Arc-goal.lua
@@ -52,7 +52,7 @@ des.region(selection.area(35,16,36,17), "unlit")
 des.region(selection.area(38,13,38,17), "unlit")
 des.region(selection.area(40,13,41,14), "unlit")
 des.region(selection.area(40,16,41,17), "unlit")
-des.region({ region={43,13, 50,15}, lit=0, type="temple", prefilled=0 })
+des.region({ region={43,13, 50,15}, lit=0, type="temple", filled=2 })
 des.region(selection.area(52,13,52,15), "unlit")
 -- Stairs
 des.stair("up", 38,10)
diff --git a/dat/Arc-loca.lua b/dat/Arc-loca.lua
index 31776ac52..93ab61fee 100644
--- a/dat/Arc-loca.lua
+++ b/dat/Arc-loca.lua
@@ -31,18 +31,18 @@ des.map([[
 ]]);
 -- Dungeon Description
 des.region(selection.area(00,00,75,19), "lit")
-des.region({ region={25,04, 28,07}, lit=1, type="temple", prefilled=0 })
-des.region({ region={25,09, 28,11}, lit=0, type="temple", prefilled=0 })
-des.region({ region={25,13, 28,16}, lit=1, type="temple", prefilled=0 })
+des.region({ region={25,04, 28,07}, lit=1, type="temple", filled=2 })
+des.region({ region={25,09, 28,11}, lit=0, type="temple", filled=2 })
+des.region({ region={25,13, 28,16}, lit=1, type="temple", filled=2 })
 des.region(selection.area(30,04,30,16), "lit")
 des.region(selection.area(32,04,32,16), "unlit")
-des.region({ region={33,04, 53,04}, lit=0, type="ordinary", prefilled=0, irregular=1 })
+des.region({ region={33,04, 53,04}, lit=0, type="ordinary", irregular=1 })
 des.region(selection.area(36,10,37,10), "unlit")
 des.region(selection.area(39,09,39,11), "unlit")
-des.region({ region={36,06, 42,08}, lit=0, type="ordinary", prefilled=0, irregular=1 })
-des.region({ region={36,12, 42,14}, lit=0, type="ordinary", prefilled=0, irregular=1 })
+des.region({ region={36,06, 42,08}, lit=0, type="ordinary", irregular=1 })
+des.region({ region={36,12, 42,14}, lit=0, type="ordinary", irregular=1 })
 des.region(selection.area(46,06,51,09), "unlit")
-des.region({ region={46,11, 49,11}, lit=0, type="ordinary", prefilled=0, irregular=1 })
+des.region({ region={46,11, 49,11}, lit=0, type="ordinary", irregular=1 })
 des.region(selection.area(48,13,51,14), "unlit")
 -- Doors
 des.door("closed",31,04)
diff --git a/dat/Cav-loca.lua b/dat/Cav-loca.lua
index 8406a5dd6..a9dfe1a07 100644
--- a/dat/Cav-loca.lua
+++ b/dat/Cav-loca.lua
@@ -31,7 +31,7 @@ des.map([[
 ]]);
 -- Dungeon Description
 des.region(selection.area(00,00,75,19), "unlit")
-des.region({ region={52,06, 73,15}, lit=1, type="ordinary", prefilled=0, irregular=1 })
+des.region({ region={52,06, 73,15}, lit=1, type="ordinary", irregular=1 })
 -- Doors
 des.door("locked",28,11)
 -- Stairs
diff --git a/dat/Cav-strt.lua b/dat/Cav-strt.lua
index 1dfe83628..83c071d0c 100644
--- a/dat/Cav-strt.lua
+++ b/dat/Cav-strt.lua
@@ -37,14 +37,14 @@ des.map([[
 ]]);
 -- Dungeon Description
 des.region(selection.area(00,00,75,19), "unlit")
-des.region({ region={13,01, 40,05}, lit=1, type="temple", prefilled=0, irregular=1 })
+des.region({ region={13,01, 40,05}, lit=1, type="temple", filled=1, irregular=1 })
 -- The occupied rooms.
-des.region({ region={02,01, 08,03}, lit=1, type="ordinary", prefilled=0, irregular=1 })
-des.region({ region={01,11, 06,14}, lit=1, type="ordinary", prefilled=0, irregular=1 })
-des.region({ region={13,08, 18,10}, lit=1, type="ordinary", prefilled=0, irregular=1 })
-des.region({ region={05,17, 14,18}, lit=1, type="ordinary", prefilled=0, irregular=1 })
-des.region({ region={17,16, 23,18}, lit=1, type="ordinary", prefilled=0, irregular=1 })
-des.region({ region={35,16, 44,18}, lit=1, type="ordinary", prefilled=0, irregular=1 })
+des.region({ region={02,01, 08,03}, lit=1, type="ordinary", irregular=1 })
+des.region({ region={01,11, 06,14}, lit=1, type="ordinary", irregular=1 })
+des.region({ region={13,08, 18,10}, lit=1, type="ordinary", irregular=1 })
+des.region({ region={05,17, 14,18}, lit=1, type="ordinary", irregular=1 })
+des.region({ region={17,16, 23,18}, lit=1, type="ordinary", irregular=1 })
+des.region({ region={35,16, 44,18}, lit=1, type="ordinary", irregular=1 })
 -- Stairs
 des.stair("down", 02,03)
 -- Portal arrival point
diff --git a/dat/Kni-strt.lua b/dat/Kni-strt.lua
index 7d43f61c4..4442d93a7 100644
--- a/dat/Kni-strt.lua
+++ b/dat/Kni-strt.lua
@@ -36,7 +36,7 @@ des.map([[
 -- Dungeon Description
 des.region(selection.area(00,00,49,15), "lit")
 des.region(selection.area(04,04,45,11), "unlit")
-des.region({ region={06,06,22,09}, lit=1, type="throne", prefilled=1 })
+des.region({ region={06,06,22,09}, lit=1, type="throne", filled=2 })
 des.region(selection.area(27,06,43,09), "lit")
 -- Portal arrival point
 des.levregion({ region = {20,14,20,14}, type="branch" })
diff --git a/dat/Pri-loca.lua b/dat/Pri-loca.lua
index 9ebd55300..5583ac270 100644
--- a/dat/Pri-loca.lua
+++ b/dat/Pri-loca.lua
@@ -26,11 +26,11 @@ des.map([[
 ........................................
 ]]);
 -- Dungeon Description
-des.region({ region={00,00, 09,13}, lit=0, type="morgue", prefilled=0 })
-des.region({ region={09,00, 30,01}, lit=0, type="morgue", prefilled=0 })
-des.region({ region={09,12, 30,13}, lit=0, type="morgue", prefilled=0 })
-des.region({ region={31,00, 39,13}, lit=0, type="morgue", prefilled=0 })
-des.region({ region={11,03, 29,10}, lit=1, type="temple", prefilled=0, irregular=1 })
+des.region({ region={00,00, 09,13}, lit=0, type="morgue", filled=1 })
+des.region({ region={09,00, 30,01}, lit=0, type="morgue", filled=1 })
+des.region({ region={09,12, 30,13}, lit=0, type="morgue", filled=1 })
+des.region({ region={31,00, 39,13}, lit=0, type="morgue", filled=1 })
+des.region({ region={11,03, 29,10}, lit=1, type="temple", filled=1, irregular=1 })
 -- The altar inside the temple
 des.altar({ x=20,y=07, align="noalign", type="shrine" })
 des.monster({ id = "aligned priest", x=20, y=07, align="noalign", peaceful = 0 })
diff --git a/dat/Sam-strt.lua b/dat/Sam-strt.lua
index ec865ab5d..8186c3cb4 100644
--- a/dat/Sam-strt.lua
+++ b/dat/Sam-strt.lua
@@ -37,7 +37,7 @@ des.map([[
 ]]);
 -- Dungeon Description
 des.region(selection.area(00,00,75,19), "lit")
-des.region({ region={18,03, 26,07}, lit=1, type="throne", prefilled=1 })
+des.region({ region={18,03, 26,07}, lit=1, type="throne", filled=2 })
 -- Portal arrival zone
 des.levregion({ region = {62,12,70,17}, type="branch" })
 -- Stairs
diff --git a/dat/Tou-loca.lua b/dat/Tou-loca.lua
index d32a7911f..808d45faa 100644
--- a/dat/Tou-loca.lua
+++ b/dat/Tou-loca.lua
@@ -32,14 +32,14 @@ des.map([[
 des.region(selection.area(00,00,75,19), "lit")
 des.non_diggable(selection.area(00,00,75,19))
 --
-des.region({ region={01,01, 04,05}, lit=0, type="morgue", prefilled = 0 })
-des.region({ region={15,03, 20,05}, lit=1, type="shop", prefilled = 0  })
-des.region({ region={62,03, 71,04}, lit=1, type="shop", prefilled = 0  })
-des.region({ region={01,17, 11,18}, lit=1, type="barracks", prefilled = 0  })
-des.region({ region={12,09, 20,10}, lit=1, type="barracks", prefilled = 0  })
-des.region({ region={53,11, 59,14}, lit=1, type="zoo", prefilled = 0  })
-des.region({ region={63,14, 72,16}, lit=1, type="barracks", prefilled = 0  })
-des.region({ region={32,14, 40,16}, lit=1, type="temple", prefilled = 0  })
+des.region({ region={01,01, 04,05}, lit=0, type="morgue", filled=1 })
+des.region({ region={15,03, 20,05}, lit=1, type="shop", filled=1 })
+des.region({ region={62,03, 71,04}, lit=1, type="shop", filled=1 })
+des.region({ region={01,17, 11,18}, lit=1, type="barracks", filled=1 })
+des.region({ region={12,09, 20,10}, lit=1, type="barracks", filled=1 })
+des.region({ region={53,11, 59,14}, lit=1, type="zoo", filled=1 })
+des.region({ region={63,14, 72,16}, lit=1, type="barracks", filled=1 })
+des.region({ region={32,14, 40,16}, lit=1, type="temple", filled=1 })
 --
 des.region({ region = {06,01,11,02}, type = "ordinary" })
 des.region({ region = {24,01,29,02}, type = "ordinary" })
diff --git a/dat/Tou-strt.lua b/dat/Tou-strt.lua
index 60891c8c4..c5efa0d29 100644
--- a/dat/Tou-strt.lua
+++ b/dat/Tou-strt.lua
@@ -36,7 +36,7 @@ des.map([[
 ]]);
 -- Dungeon Description
 des.region(selection.area(00,00,75,19), "lit")
-des.region({ region={14,01, 20,03}, lit=0, type="morgue", prefilled=0 })
+des.region({ region={14,01, 20,03}, lit=0, type="morgue", filled=1 })
 des.region(selection.area(07,10,11,12), "unlit")
 des.region(selection.area(04,16,08,18), "unlit")
 des.region(selection.area(17,16,21,18), "unlit")
diff --git a/dat/Wiz-loca.lua b/dat/Wiz-loca.lua
index 6acc15da6..7197f1856 100644
--- a/dat/Wiz-loca.lua
+++ b/dat/Wiz-loca.lua
@@ -36,18 +36,18 @@ des.replace_terrain({ region = {34, 1,68,19}, fromterrain="}", toterrain=".", ch
 
 -- Dungeon Description
 des.region(selection.area(00,00,75,20), "lit")
-des.region({ region={37,04,65,16}, lit=0, type="ordinary", prefilled=1, irregular=1,
+des.region({ region={37,04,65,16}, lit=0, type="ordinary", irregular=1,
              contents = function()
                 des.door({ state="secret", wall="random" })
                 end
 })
-des.region({ region={39,06,63,14}, lit=0, type="ordinary", prefilled=1, irregular=1,
+des.region({ region={39,06,63,14}, lit=0, type="ordinary", irregular=1,
              contents = function()
                 des.door({ state="secret", wall="random" })
              end
 })
 
-des.region({ region={41,08,46,12}, lit=1, type="ordinary", prefilled=1, irregular=1,
+des.region({ region={41,08,46,12}, lit=1, type="ordinary", irregular=1,
              contents = function()
                 local walls = { "north", "south", "west" }
                 local widx = math.random(1, #walls)
@@ -55,7 +55,7 @@ des.region({ region={41,08,46,12}, lit=1, type="ordinary", prefilled=1, irregula
              end
 })
 
-des.region({ region={56,08,61,12}, lit=1, type="ordinary", prefilled=1, irregular=1,
+des.region({ region={56,08,61,12}, lit=1, type="ordinary", irregular=1,
              contents = function()
                 local walls = { "north", "south", "east" }
                 local widx = math.random(1, #walls)
@@ -66,7 +66,7 @@ des.region({ region={56,08,61,12}, lit=1, type="ordinary", prefilled=1, irregula
 des.region(selection.area(48,08,54,08), "unlit")
 des.region(selection.area(48,12,54,12), "unlit")
 
-des.region({ region={48,10,54,10}, lit=0, type="ordinary", prefilled=1, irregular=1,
+des.region({ region={48,10,54,10}, lit=0, type="ordinary", irregular=1,
              contents = function()
                 des.door({ state="secret", wall="random" })
              end
diff --git a/dat/Wiz-strt.lua b/dat/Wiz-strt.lua
index fdc9ae531..715cb5744 100644
--- a/dat/Wiz-strt.lua
+++ b/dat/Wiz-strt.lua
@@ -44,7 +44,7 @@ des.replace_terrain({ region={13,5, 33,15}, fromterrain="C", toterrain=".", chan
 des.region(selection.area(00,00,75,19), "lit")
 des.region(selection.area(35,00,49,03), "unlit")
 des.region(selection.area(43,12,49,16), "unlit")
-des.region({ region={19,11,33,15}, lit=0, type="ordinary", prefilled=0, irregular=1 })
+des.region({ region={19,11,33,15}, lit=0, type="ordinary", irregular=1 })
 des.region(selection.area(30,10,31,10), "unlit")
 -- Stairs
 des.stair("down", 30,10)
diff --git a/dat/astral.lua b/dat/astral.lua
index 7085eba78..cfe22dd78 100644
--- a/dat/astral.lua
+++ b/dat/astral.lua
@@ -76,9 +76,9 @@ place:set(51,9);
 -- Where the player will land on arrival
 des.teleport_region({ region = {29,15,45,15}, exclude = {30,15,44,15} })
 -- Lit courts
-des.region({ region={01,05,16,14},lit=1,type="ordinary",prefilled=1,irregular=1 })
-des.region({ region={31,01,44,10},lit=1,type="ordinary",prefilled=1,irregular=1 })
-des.region({ region={61,05,74,14},lit=1,type="ordinary",prefilled=1,irregular=1 })
+des.region({ region={01,05,16,14},lit=1,type="ordinary",irregular=1 })
+des.region({ region={31,01,44,10},lit=1,type="ordinary",irregular=1 })
+des.region({ region={61,05,74,14},lit=1,type="ordinary",irregular=1 })
 -- A Sanctum for each alignment
 -- The shrines' alignments are shuffled for
 -- each game
diff --git a/dat/castle.lua b/dat/castle.lua
index 4c614f550..c2f05f02f 100644
--- a/dat/castle.lua
+++ b/dat/castle.lua
@@ -230,7 +230,7 @@ des.region(selection.area(00,00,62,16),"unlit")
 des.region(selection.area(00,05,05,11),"lit")
 des.region(selection.area(57,05,62,11),"lit")
 --   Throne room
-des.region({ region={27,05, 37,11},lit=1,type="throne", prefilled=1 })
+des.region({ region={27,05, 37,11},lit=1,type="throne", filled=2 })
 --   Antechamber
 des.region(selection.area(07,05,14,11),"lit")
 --   Storerooms
@@ -244,8 +244,8 @@ des.region(selection.area(56,02,60,03),"lit")
 des.region(selection.area(02,13,06,14),"lit")
 des.region(selection.area(56,13,60,14),"lit")
 --   Barracks
-des.region({ region={16,05, 25,06},lit=1,type="barracks", prefilled=0 })
-des.region({ region={16,10, 25,11},lit=1,type="barracks", prefilled=0 })
+des.region({ region={16,05, 25,06},lit=1,type="barracks", filled=1 })
+des.region({ region={16,10, 25,11},lit=1,type="barracks", filled=1 })
 --   Hallways
 des.region(selection.area(08,03,54,03),"unlit")
 des.region(selection.area(08,13,54,13),"unlit")
diff --git a/dat/fakewiz1.lua b/dat/fakewiz1.lua
index 6576176e2..906d7f97c 100644
--- a/dat/fakewiz1.lua
+++ b/dat/fakewiz1.lua
@@ -23,7 +23,7 @@ des.levregion({ region={01,00,79,20}, region_islev=1, exclude={0,0,8,7}, type="b
 des.teleport_region({ region={01,00,79,20}, region_islev=1,exclude={2,2,6,6} })
 des.levregion({ region={4,4,4,4}, type="portal", name="wizard3" })
 des.mazewalk(08,05,"east")
-des.region({ region={04,03,06,06},lit=0,type="ordinary",prefilled=0,irregular=1 })
+des.region({ region={04,03,06,06},lit=0,type="ordinary",irregular=1,arrival_room=true })
 des.monster("L",04,04)
 des.monster("vampire lord",03,04)
 des.monster("kraken",06,06)
diff --git a/dat/fakewiz2.lua b/dat/fakewiz2.lua
index f34d00af0..ae14a6966 100644
--- a/dat/fakewiz2.lua
+++ b/dat/fakewiz2.lua
@@ -22,7 +22,6 @@ des.levregion({ region={01,00,79,20}, region_islev=1, exclude={0,0,8,7}, type="s
 des.levregion({ region={01,00,79,20}, region_islev=1, exclude={0,0,8,7}, type="branch" });
 des.teleport_region({ region={01,00,79,20}, region_islev=1,exclude={2,2,6,6} })
 des.mazewalk(08,05,"east")
-des.region({ region={04,03,06,06},lit=0,type="ordinary",prefilled=0,irregular=1 })
 des.monster("L",04,04)
 des.monster("vampire lord",03,04)
 des.monster("kraken",06,06)
diff --git a/dat/knox.lua b/dat/knox.lua
index c1b4c204b..e9603e866 100644
--- a/dat/knox.lua
+++ b/dat/knox.lua
@@ -39,7 +39,7 @@ des.levregion({ region = {08,16,08,16}, type="branch" });
 des.teleport_region({ region = {06,15,09,16}, dir="up" })
 des.teleport_region({ region = {06,15,09,16}, dir="down" })
 --   Throne room, with Croesus on the throne
-des.region({ x1=37,y1=08,x2=46,y2=11, lit=1, type="throne", prefilled=0 })
+des.region({ x1=37,y1=08,x2=46,y2=11, lit=1, type="throne", filled=1 })
 --   50% chance each to move throne and/or fort's entry secret door up one row
 if percent(50) then
    des.monster({ id = "Croesus", x=43, y=10, peaceful = 0 })
@@ -80,10 +80,10 @@ des.region(selection.area(46,06,48,06),"lit")
 des.region(selection.area(19,13,21,13),"lit")
 des.region(selection.area(46,13,48,13),"lit")
 --   A welcoming committee
-des.region({ region={03,10,07,13},lit=1,type="zoo",prefilled=0,irregular=1 })
+des.region({ region={03,10,07,13},lit=1,type="zoo",filled=1,irregular=1 })
 --   arrival chamber; needs to be a real room to control migrating monsters,
 --   and `unfilled' is a kludge to force an ordinary room to remain a room
-des.region({ region={06,15,09,16},lit=0,type="ordinary",prefilled=0 })
+des.region({ region={06,15,09,16},lit=0,type="ordinary",arrival_room=true })
 
 --   3.6.2:  Entering level carrying a lit candle would show the whole entry
 --   chamber except for its top right corner even though some of the revealed
@@ -109,7 +109,7 @@ des.region(selection.area(05,14,09,14),"unlit")
 --   it is expected to work.)
 
 --   Barracks
-des.region({ region={62,03,71,04},lit=1,type="barracks",prefilled=0,irregular=1 })
+des.region({ region={62,03,71,04},lit=1,type="barracks",filled=1,irregular=1 })
 -- Doors
 des.door("closed",06,14)
 des.door("closed",09,03)
diff --git a/dat/medusa-1.lua b/dat/medusa-1.lua
index 63a471904..f97100811 100644
--- a/dat/medusa-1.lua
+++ b/dat/medusa-1.lua
@@ -36,8 +36,8 @@ des.map([[
 -- Dungeon Description
 des.region(selection.area(00,00,74,19),"lit")
 des.region(selection.area(31,07,45,07),"unlit")
--- (must maintain one room definition; `filled=0' forces its room to be kept)
-des.region({ region={35,09, 41,10}, lit = 0, type="ordinary", prefilled = 1 })
+-- make the downstairs room a real room to control arriving monsters
+des.region({ region={35,09, 41,10}, lit = 0, type="ordinary", arrival_room=true })
 des.region(selection.area(31,12,45,12),"unlit")
 -- Teleport: down to up stairs island, up to Medusa's island
 des.teleport_region({ region = {01,01,05,17}, dir="down" })
diff --git a/dat/medusa-2.lua b/dat/medusa-2.lua
index 4b03631e7..017b9b4b3 100644
--- a/dat/medusa-2.lua
+++ b/dat/medusa-2.lua
@@ -32,9 +32,10 @@ des.map([[
 -- Dungeon Description
 des.region(selection.area(00,00,74,19),"lit")
 des.region(selection.area(02,03,05,16),"unlit")
-des.region({ region={61,03, 72,16}, lit=0, type="ordinary", prefilled = 1,irregular = 1 })
+des.region({ region={61,03, 72,16}, lit=0, type="ordinary",irregular = 1 })
 des.region(selection.area(71,08,72,11),"unlit")
-des.region(selection.area(67,08,69,11),"lit")
+-- make the downstairs area a real room to control arriving monsters
+des.region({ region={67,08,69,11}, lit=1, type="ordinary", arrival_room=true })
 -- Teleport: down to up stairs island, up to Medusa's island
 des.teleport_region({ region = {02,03,05,16}, dir="down" })
 des.teleport_region({ region = {61,03,72,16}, dir="up" })
diff --git a/dat/medusa-3.lua b/dat/medusa-3.lua
index 221cb8172..56f37c1c7 100644
--- a/dat/medusa-3.lua
+++ b/dat/medusa-3.lua
@@ -37,7 +37,7 @@ place:set(66,05);
 place:set(46,15);
 
 des.region(selection.area(00,00,74,19),"lit")
-des.region({ region={49,14, 51,16}, lit=-1, type="ordinary", prefilled = 1 });
+des.region({ region={49,14, 51,16}, lit=-1, type="ordinary" });
 des.region(selection.area(07,05,09,07),"unlit")
 des.region(selection.area(65,04,67,06),"unlit")
 des.region(selection.area(45,14,47,16),"unlit")
diff --git a/dat/medusa-4.lua b/dat/medusa-4.lua
index c5f8e206d..7df55430c 100644
--- a/dat/medusa-4.lua
+++ b/dat/medusa-4.lua
@@ -40,7 +40,6 @@ place:set(10,08);
 place:set(10,12);
 --
 des.region(selection.area(00,00,74,19),"lit")
-des.region({ region={13,03, 18,13}, lit=1, type="ordinary", prefilled=1 })
 --
 des.teleport_region({ region = {64,01,74,17}, dir="down" });
 des.teleport_region({ region = {02,02,18,13}, dir="up" });
diff --git a/dat/minend-1.lua b/dat/minend-1.lua
index 30e1a23d7..f86140518 100644
--- a/dat/minend-1.lua
+++ b/dat/minend-1.lua
@@ -35,8 +35,8 @@ des.map([[
 local place = { {08,16},{13,07},{21,08},{41,14},{50,04},{50,16},{66,01} }
 shuffle(place)
 
-des.region({ region={26,01,32,01}, lit=0, type="ordinary",
-	     prefilled=0, irregular=1 })
+-- make the entry chamber a real room; it affects monster arrival
+des.region({ region={26,01,32,01}, lit=0, type="ordinary", irregular=1, arrival_room=true })
 des.region(selection.area(20,08,21,08),"unlit")
 des.region(selection.area(23,08,25,08),"unlit");
 -- Secret doors
diff --git a/dat/minetn-5.lua b/dat/minetn-5.lua
index 5faac05a1..8160cef07 100644
--- a/dat/minetn-5.lua
+++ b/dat/minetn-5.lua
@@ -95,13 +95,13 @@ des.monster("dwarf")
 des.monster("dwarf")
 
 -- The shops
-des.region({ region={25,17, 28,19}, lit=1, type="candle shop", prefilled=0 })
+des.region({ region={25,17, 28,19}, lit=1, type="candle shop", filled=1 })
 des.door("closed",24,18)
-des.region({ region={59, 9, 67,10}, lit=1, type="shop", prefilled=0 })
+des.region({ region={59, 9, 67,10}, lit=1, type="shop", filled=1 })
 des.door("closed",66,08)
-des.region({ region={57,13, 60,15}, lit=1, type="tool shop", prefilled=0 })
+des.region({ region={57,13, 60,15}, lit=1, type="tool shop", filled=1 })
 des.door("closed",56,14)
-des.region({ region={05,09, 08,10}, lit=1, type=monkfoodshop(), prefilled=0 })
+des.region({ region={05,09, 08,10}, lit=1, type=monkfoodshop(), filled=1 })
 des.door("closed",07,11)
 -- Gnome homes
 des.door("closed",04,14)
diff --git a/dat/minetn-6.lua b/dat/minetn-6.lua
index 7e3c88131..ba642c625 100644
--- a/dat/minetn-6.lua
+++ b/dat/minetn-6.lua
@@ -36,11 +36,11 @@ des.levregion({ type="stair-down", region={61,03,75,19}, region_islev=1, exclude
 des.feature("fountain" ,22,07)
 des.feature("fountain", 09,13)
 des.region(selection.area(13,5,14,6),"unlit")
-des.region({ region={09,07, 11,09}, lit=1, type="candle shop", prefilled=0 })
-des.region({ region={16,04, 18,06}, lit=1, type="tool shop", prefilled=0 })
-des.region({ region={23,01, 25,03}, lit=1, type="shop", prefilled=0 })
-des.region({ region={22,12, 24,13}, lit=1, type=monkfoodshop(), prefilled=0 })
-des.region({ region={31,12, 36,14}, lit=1, type="temple", prefilled=0 })
+des.region({ region={09,07, 11,09}, lit=1, type="candle shop", filled=1 })
+des.region({ region={16,04, 18,06}, lit=1, type="tool shop", filled=1 })
+des.region({ region={23,01, 25,03}, lit=1, type="shop", filled=1 })
+des.region({ region={22,12, 24,13}, lit=1, type=monkfoodshop(), filled=1 })
+des.region({ region={31,12, 36,14}, lit=1, type="temple", filled=1 })
 des.altar({ x=35,y=13,align=align[1],type="shrine"})
 
 des.door("closed",5,2)
diff --git a/dat/orcus.lua b/dat/orcus.lua
index b04247491..109053c3d 100644
--- a/dat/orcus.lua
+++ b/dat/orcus.lua
@@ -77,9 +77,9 @@ des.door("open",26,14)
 des.door("closed",06,15)
 -- Special rooms
 des.altar({ x=24,y=07,align="noalign",type="sanctum" })
-des.region({ region={22,12,25,16},lit=0,type="morgue", prefilled=0 })
-des.region({ region={32,09,37,12},lit=1,type="shop",prefilled=0 })
-des.region({ region={12,00,15,04},lit=1,type="shop",prefilled=0 })
+des.region({ region={22,12,25,16},lit=0,type="morgue",filled=1 })
+des.region({ region={32,09,37,12},lit=1,type="shop",filled=1 })
+des.region({ region={12,00,15,04},lit=1,type="shop",filled=1 })
 -- Some traps.
 des.trap("spiked pit")
 des.trap("sleep gas")
diff --git a/dat/sanctum.lua b/dat/sanctum.lua
index c99eff81d..84f7f7f99 100644
--- a/dat/sanctum.lua
+++ b/dat/sanctum.lua
@@ -36,7 +36,7 @@ des.region({ region={15,07, 21,10}, lit=1, type="temple", contents = function()
                 des.door({ wall = "random", state = "secret" });
 end })
 des.altar({ x=18, y=08, align="noalign", type="sanctum" })
-des.region({ region={41,06, 48,11}, lit=0, type="morgue", prefilled=0, irregular=1 })
+des.region({ region={41,06, 48,11}, lit=0, type="morgue", filled=1, irregular=1 })
 -- Non diggable walls
 des.non_diggable(selection.area(00,00,75,19))
 -- Invisible barrier separating the left & right halves of the level
diff --git a/dat/soko1-1.lua b/dat/soko1-1.lua
index f38667960..1d6b7c09b 100644
--- a/dat/soko1-1.lua
+++ b/dat/soko1-1.lua
@@ -94,8 +94,7 @@ des.door("closed", 17, 11);
 des.door("closed", 17, 13);
 des.door("closed", 17, 15);
 
-des.region({ region={18,10, 22,16}, lit = 1, type = "zoo",
-	     prefilled = 0, irregular = 1 });
+des.region({ region={18,10, 22,16}, lit = 1, type = "zoo", filled = 1, irregular = 1 });
 
 px, py = selection.rndcoord(place);
 if percent(75) then
diff --git a/dat/soko1-2.lua b/dat/soko1-2.lua
index 48305895e..3b54a231e 100644
--- a/dat/soko1-2.lua
+++ b/dat/soko1-2.lua
@@ -96,8 +96,7 @@ des.door("locked",23,12)
 des.door("closed",17,10)
 des.door("closed",17,12)
 des.door("closed",17,14)
-des.region({ region={18,09, 22,15}, lit = 1, type = "zoo",
-	     prefilled = 0, irregular = 1 });
+des.region({ region={18,09, 22,15}, lit = 1, type = "zoo", filled = 1, irregular = 1 });
 
 px, py = selection.rndcoord(place);
 if percent(25) then
diff --git a/dat/themerms.lua b/dat/themerms.lua
index 4b3947fe4..85c3e18f4 100644
--- a/dat/themerms.lua
+++ b/dat/themerms.lua
@@ -12,7 +12,6 @@
 -- core calls themerooms_generate() multiple times per level
 -- to generate a single themed room.
 
-
 themerooms = {
   {
      -- the "default" room
@@ -263,7 +262,7 @@ themerooms = {
 |......|
 |......|
 |......|
---------]], contents = function(m) des.region({ region={1,1,3,3}, type="ordinary", irregular=true, prefilled=true }); end });
+--------]], contents = function(m) des.region({ region={1,1,3,3}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- L-shaped, rot 1
@@ -276,7 +275,7 @@ xxx|...|
 |......|
 |......|
 |......|
---------]], contents = function(m) des.region({ region={5,1,5,3}, type="ordinary", irregular=true, prefilled=true }); end });
+--------]], contents = function(m) des.region({ region={5,1,5,3}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- L-shaped, rot 2
@@ -289,7 +288,7 @@ xxx|...|
 ----...|
 xxx|...|
 xxx|...|
-xxx-----]], contents = function(m) des.region({ region={1,1,2,2}, type="ordinary", irregular=true, prefilled=true }); end });
+xxx-----]], contents = function(m) des.region({ region={1,1,2,2}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- L-shaped, rot 3
@@ -302,7 +301,7 @@ xxx-----]], contents = function(m) des.region({ region={1,1,2,2}, type="ordinary
 |...----
 |...|xxx
 |...|xxx
------xxx]], contents = function(m) des.region({ region={1,1,2,2}, type="ordinary", irregular=true, prefilled=true }); end });
+-----xxx]], contents = function(m) des.region({ region={1,1,2,2}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- Blocked center
@@ -324,7 +323,7 @@ if (percent(30)) then
    shuffle(terr);
    des.replace_terrain({ region = {1,1, 9,9}, fromterrain = "L", toterrain = terr[1] });
 end
-des.region({ region={1,1,2,2}, type="ordinary", irregular=true, prefilled=true });
+des.region({ region={1,1,2,2}, type="ordinary", irregular=true, filled=1 });
 end });
    end,
 
@@ -337,7 +336,7 @@ x--.--x
 |.....|
 --...--
 x--.--x
-xx---xx]], contents = function(m) des.region({ region={3,3,3,3}, type="ordinary", irregular=true, prefilled=true }); end });
+xx---xx]], contents = function(m) des.region({ region={3,3,3,3}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- Circular, medium
@@ -351,7 +350,7 @@ x--...--x
 |.......|
 --.....--
 x--...--x
-xx-----xx]], contents = function(m) des.region({ region={4,4,4,4}, type="ordinary", irregular=true, prefilled=true }); end });
+xx-----xx]], contents = function(m) des.region({ region={4,4,4,4}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- Circular, big
@@ -367,7 +366,7 @@ x-.......-x
 --.......--
 x-.......-x
 x---...---x
-xxx-----xxx]], contents = function(m) des.region({ region={5,5,5,5}, type="ordinary", irregular=true, prefilled=true }); end });
+xxx-----xxx]], contents = function(m) des.region({ region={5,5,5,5}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- T-shaped
@@ -380,7 +379,7 @@ xxx|...|xxx
 |.........|
 |.........|
 |.........|
------------]], contents = function(m) des.region({ region={5,5,5,5}, type="ordinary", irregular=true, prefilled=true }); end });
+-----------]], contents = function(m) des.region({ region={5,5,5,5}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- T-shaped, rot 1
@@ -396,7 +395,7 @@ xxx|...|xxx
 |...----
 |...|xxx
 |...|xxx
------xxx]], contents = function(m) des.region({ region={2,2,2,2}, type="ordinary", irregular=true, prefilled=true }); end });
+-----xxx]], contents = function(m) des.region({ region={2,2,2,2}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- T-shaped, rot 2
@@ -409,7 +408,7 @@ xxx|...|xxx
 ----...----
 xxx|...|xxx
 xxx|...|xxx
-xxx-----xxx]], contents = function(m) des.region({ region={2,2,2,2}, type="ordinary", irregular=true, prefilled=true }); end });
+xxx-----xxx]], contents = function(m) des.region({ region={2,2,2,2}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- T-shaped, rot 3
@@ -425,7 +424,7 @@ xxx|...|
 ----...|
 xxx|...|
 xxx|...|
-xxx-----]], contents = function(m) des.region({ region={5,5,5,5}, type="ordinary", irregular=true, prefilled=true }); end });
+xxx-----]], contents = function(m) des.region({ region={5,5,5,5}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- S-shaped
@@ -441,7 +440,7 @@ xxx-----]], contents = function(m) des.region({ region={5,5,5,5}, type="ordinary
 ----...|
 xxx|...|
 xxx|...|
-xxx-----]], contents = function(m) des.region({ region={2,2,2,2}, type="ordinary", irregular=true, prefilled=true }); end });
+xxx-----]], contents = function(m) des.region({ region={2,2,2,2}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- S-shaped, rot 1
@@ -454,7 +453,7 @@ xxx|......|
 |......----
 |......|xxx
 |......|xxx
---------xxx]], contents = function(m) des.region({ region={5,5,5,5}, type="ordinary", irregular=true, prefilled=true }); end });
+--------xxx]], contents = function(m) des.region({ region={5,5,5,5}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- Z-shaped
@@ -470,7 +469,7 @@ xxx|...|
 |...----
 |...|xxx
 |...|xxx
------xxx]], contents = function(m) des.region({ region={5,5,5,5}, type="ordinary", irregular=true, prefilled=true }); end });
+-----xxx]], contents = function(m) des.region({ region={5,5,5,5}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- Z-shaped, rot 1
@@ -483,7 +482,7 @@ xxx|...|
 ----......|
 xxx|......|
 xxx|......|
-xxx--------]], contents = function(m) des.region({ region={2,2,2,2}, type="ordinary", irregular=true, prefilled=true }); end });
+xxx--------]], contents = function(m) des.region({ region={2,2,2,2}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- Cross
@@ -499,7 +498,7 @@ xxx|...|xxx
 ----...----
 xxx|...|xxx
 xxx|...|xxx
-xxx-----xxx]], contents = function(m) des.region({ region={6,6,6,6}, type="ordinary", irregular=true, prefilled=true }); end });
+xxx-----xxx]], contents = function(m) des.region({ region={6,6,6,6}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- Four-leaf clover
@@ -515,7 +514,7 @@ xx|.....|xx
 |.........|
 |...---...|
 |...|x|...|
------x-----]], contents = function(m) des.region({ region={6,6,6,6}, type="ordinary", irregular=true, prefilled=true }); end });
+-----x-----]], contents = function(m) des.region({ region={6,6,6,6}, type="ordinary", irregular=true, filled=1 }); end });
    end,
 
    -- Water-surrounded vault
@@ -526,7 +525,7 @@ xx|.....|xx
 }|..|}
 }|..|}
 }----}
-}}}}}}]], contents = function(m) des.region({ region={3,3,3,3}, type="themed", irregular=true, prefilled=false, joined=false });
+}}}}}}]], contents = function(m) des.region({ region={3,3,3,3}, type="themed", irregular=true, filled=0, joined=false });
      local nasty_undead = { "giant zombie", "ettin zombie", "vampire lord" };
      des.object("chest", 2, 2);
      des.object("chest", 3, 2);
diff --git a/dat/valley.lua b/dat/valley.lua
index f283cb415..b030925f7 100644
--- a/dat/valley.lua
+++ b/dat/valley.lua
@@ -53,9 +53,9 @@ end
 -- The shrine to Moloch.
 des.region({ region={01,06, 05,14},lit=1,type="temple" })
 -- The Morgues
-des.region({ region={19,01, 24,08},lit=0,type="morgue",prefilled=0,irregular=1 })
-des.region({ region={09,14, 16,18},lit=0,type="morgue",prefilled=0,irregular=1 })
-des.region({ region={37,09, 43,14},lit=0,type="morgue",prefilled=0,irregular=1 })
+des.region({ region={19,01, 24,08},lit=0,type="morgue",filled=1,irregular=1 })
+des.region({ region={09,14, 16,18},lit=0,type="morgue",filled=1,irregular=1 })
+des.region({ region={37,09, 43,14},lit=0,type="morgue",filled=1,irregular=1 })
 -- Stairs
 des.stair("down", 01,01)
 -- Branch location
diff --git a/dat/wizard1.lua b/dat/wizard1.lua
index 3a40d6ae9..2e4a0af79 100644
--- a/dat/wizard1.lua
+++ b/dat/wizard1.lua
@@ -28,12 +28,12 @@ des.levregion({ type="stair-up", region={01,00,79,20}, region_islev=1, exclude={
 des.levregion({ type="stair-down", region={01,00,79,20}, region_islev=1, exclude={0,0,28,12} })
 des.levregion({ type="branch", region={01,00,79,20}, region_islev=1, exclude={0,0,28,12} })
 des.teleport_region({ region={01,00,79,20}, region_islev=1, exclude={0,0,27,12} })
-des.region({ region={12,01, 20,09}, lit=0, type="morgue", prefilled=1, contents=function()
+des.region({ region={12,01, 20,09}, lit=0, type="morgue", filled=2, contents=function()
                 local sdwall = { "south", "west", "east" };
                 des.door({ wall = sdwall[math.random(1, #sdwall)], state = "secret" });
 end })
 -- another region to constrain monster arrival
-des.region({ region={01,01, 10,11}, lit=0, type="ordinary", prefilled=0 })
+des.region({ region={01,01, 10,11}, lit=0, type="ordinary", arrival_room=true })
 des.mazewalk(28,05,"east")
 des.ladder("down", 06,05)
 -- Non diggable walls
diff --git a/dat/wizard2.lua b/dat/wizard2.lua
index d9fd181a0..825f2f342 100644
--- a/dat/wizard2.lua
+++ b/dat/wizard2.lua
@@ -26,8 +26,8 @@ des.levregion({ type="stair-down", region={01,00,79,20}, region_islev=1, exclude
 des.levregion({ type="branch", region={01,00,79,20}, region_islev=1, exclude={0,0,28,12} })
 des.teleport_region({ region={01,00,79,20}, region_islev=1, exclude={0,0,27,12} })
 -- entire tower in a region, constrains monster migration
-des.region({ region={01,01, 26,11}, lit=0, type="ordinary", prefilled=1 })
-des.region({ region={09,03, 17,09}, lit=0, type="zoo", prefilled=0 })
+des.region({ region={01,01, 26,11}, lit=0, type="ordinary", arrival_room=true })
+des.region({ region={09,03, 17,09}, lit=0, type="zoo", filled=1 })
 des.door("closed",15,02)
 des.door("closed",11,10)
 des.mazewalk(28,05,"east")
diff --git a/dat/wizard3.lua b/dat/wizard3.lua
index 60e9dd014..4f0baf922 100644
--- a/dat/wizard3.lua
+++ b/dat/wizard3.lua
@@ -27,11 +27,10 @@ des.levregion({ type="branch", region={01,00,79,20}, region_islev=1, exclude={0,
 des.teleport_region({ region={01,00,79,20}, region_islev=1, exclude={0,0,27,12} })
 des.levregion({ region={25,11,25,11}, type="portal", name="fakewiz1" });
 des.mazewalk(28,09,"east")
-des.region({ region={07,03, 15,11}, lit=0 ,type="morgue",prefilled=1 })
+des.region({ region={07,03, 15,11}, lit=0 ,type="morgue", filled=2 })
 des.region({ region={17,06, 18,11}, lit=0, type="beehive" })
--- make the entry chamber a real room; it affects monster arrival;
--- `unfilled' is a kludge to force an ordinary room to remain a room
-des.region({ region={20,06,26,11},lit=0,type="ordinary",prefilled=1,
+-- make the entry chamber a real room; it affects monster arrival
+des.region({ region={20,06,26,11},lit=0,type="ordinary",arrival_room=true,
              contents = function()
                 local w = "north";
                 if percent(50) then w = "west" end
diff --git a/doc/lua.adoc b/doc/lua.adoc
index 27da21ed9..cc4835d7b 100644
--- a/doc/lua.adoc
+++ b/doc/lua.adoc
@@ -304,13 +304,13 @@ Set flags for this level.
 | nommap        | Prevents magic mapping
 | shortsighted  | Prevents monsters from seeing the hero from far away
 | arboreal      | Notionally an outdoor map; replaces solid stone with trees
-| mazelevel     | 
+| mazelevel     |
 | shroud        | Unseen locations on the level will not be remembered by the hero, instead of rendering as out-of-sight map, trap, and object glyphs like they normally do.
 | graveyard     | Treats the level as a graveyard level (causes graveyard sounds and undead have a reduced chance of leaving corpses).
 | icedpools     | Ice generated with the level will be treated as frozen pools instead of frozen moats.
-| corrmaze      | 
+| corrmaze      |
 | premapped     | Map, including traps and boulders, is revealed on entrance.
-| solidify      | Areas outside the specified level map are made undiggable and unphaseable. 
+| solidify      | Areas outside the specified level map are made undiggable and unphaseable.
 | inaccessibles | If inaccessible areas are generated, generate ways for them to connect to the "accessible" area.
 | noflip        | Prevent flipping the level.
 | noflipx       | Prevent flipping the level horizontally.
@@ -471,7 +471,7 @@ Example:
 Example:
 
  des.region(selection, lit);
- des.region({ x1=NN, y1=NN, x2=NN, y2=NN, lit=BOOL, type=ROOMTYPE, joined=BOOL, irregular=BOOL, prefilled=BOOL [ , contents = FUNCTION ] });
+ des.region({ x1=NN, y1=NN, x2=NN, y2=NN, lit=BOOL, type=ROOMTYPE, joined=BOOL, irregular=BOOL, filled=NN [ , contents = FUNCTION ] });
  des.region({ region={x1,y1, x2,y2}, type="ordinary" });
 
 === replace_terrain
diff --git a/include/extern.h b/include/extern.h
index 79708ebfe..60c44d2fd 100644
--- a/include/extern.h
+++ b/include/extern.h
@@ -2467,7 +2467,7 @@ E boolean FDECL(create_room, (XCHAR_P, XCHAR_P, XCHAR_P, XCHAR_P, XCHAR_P,
                               XCHAR_P, XCHAR_P, XCHAR_P));
 E void FDECL(create_secret_door, (struct mkroom *, XCHAR_P));
 E boolean FDECL(dig_corridor, (coord *, coord *, BOOLEAN_P, SCHAR_P, SCHAR_P));
-E void FDECL(fill_special_room, (struct mkroom *, BOOLEAN_P));
+E void FDECL(fill_special_room, (struct mkroom *));
 E boolean FDECL(load_special, (const char *));
 E xchar FDECL(selection_getpoint, (int, int, struct selectionvar *));
 E struct selectionvar *NDECL(selection_new);
diff --git a/include/mkroom.h b/include/mkroom.h
index e7bd874ea..e707aa695 100644
--- a/include/mkroom.h
+++ b/include/mkroom.h
@@ -90,6 +90,14 @@ enum roomtype_types {
 #define ROOMOFFSET  3 /* (levl[x][y].roomno - ROOMOFFSET) gives g.rooms[] index,
                        * for inside-squares and non-shared boundaries */
 
+/* Values for needfill */
+#define FILL_NONE    0 /* do not fill this room with anything */
+#define FILL_NORMAL  1 /* fill the room normally (OROOM or THEMEROOM gets
+                          fill_ordinary_room; any other room type gets stocked
+                          with its usual monsters/objects/terrain) */
+#define FILL_LVFLAGS 2 /* special rooms only; set the room's rtype and level
+                          flags as appropriate, but do not put anything in it */
+
 #define IS_ROOM_PTR(x)      ((x) >= g.rooms && (x) < g.rooms + MAXNROFROOMS)
 #define IS_ROOM_INDEX(x)    ((x) >= 0 && (x) < MAXNROFROOMS)
 #define IS_SUBROOM_PTR(x)   ((x) >= g.subrooms && (x) < g.subrooms + MAXNROFROOMS)
diff --git a/include/sp_lev.h b/include/sp_lev.h
index 821359907..cf86388e3 100644
--- a/include/sp_lev.h
+++ b/include/sp_lev.h
@@ -185,7 +185,7 @@ typedef struct _room {
     Str_or_Len parent;
     xchar x, y, w, h;
     xchar xalign, yalign;
-    xchar rtype, chance, rlit, filled, joined;
+    xchar rtype, chance, rlit, needfill, joined;
 } room;
 
 struct mapfragment {
diff --git a/src/mklev.c b/src/mklev.c
index b4d7efe07..670f8760a 100644
--- a/src/mklev.c
+++ b/src/mklev.c
@@ -757,7 +757,7 @@ struct mkroom *croom;
         fill_ordinary_room(croom->sbrooms[x]);
     }
 
-    if (!croom->needfill)
+    if (croom->needfill != FILL_NORMAL)
         return;
 
     /* put a sleeping monster inside */
@@ -916,7 +916,7 @@ makelevel()
                      TRUE, VAULT, FALSE);
             g.level.flags.has_vault = 1;
             ++room_threshold;
-            fill_special_room(&g.rooms[g.nroom - 1], FALSE);
+            fill_special_room(&g.rooms[g.nroom - 1]);
             mk_knox_portal(g.vault_x + w, g.vault_y + h);
             if (!g.level.flags.noteleport && !rn2(3))
                 makevtele();
diff --git a/src/sp_lev.c b/src/sp_lev.c
index b3b369c73..258fa8f66 100755
--- a/src/sp_lev.c
+++ b/src/sp_lev.c
@@ -1042,10 +1042,10 @@ fill_special_rooms()
 
     for (tmpi = 0; tmpi < g.nroom; tmpi++) {
         if (g.rooms[tmpi].needfill)
-            fill_special_room(&g.rooms[tmpi], (g.rooms[tmpi].needfill == 2));
+            fill_special_room(&g.rooms[tmpi]);
         for (m = 0; m < g.rooms[tmpi].nsubrooms; m++)
             if (g.rooms[tmpi].sbrooms[m]->needfill)
-                fill_special_room(g.rooms[tmpi].sbrooms[m], FALSE);
+                fill_special_room(g.rooms[tmpi].sbrooms[m]);
     }
 }
 
@@ -2682,14 +2682,14 @@ corridor *c;
  * Fill a room (shop, zoo, etc...) with appropriate stuff.
  */
 void
-fill_special_room(croom, prefilled)
+fill_special_room(croom)
 struct mkroom *croom;
-boolean prefilled;
 {
-    if (!croom || croom->rtype == OROOM || croom->rtype == THEMEROOM)
+    if (!croom || croom->rtype == OROOM || croom->rtype == THEMEROOM
+        || croom->needfill == FILL_NONE)
         return;
 
-    if (!prefilled) {
+    if (croom->needfill == FILL_NORMAL) {
         int x, y;
 
         /* Shop ? */
@@ -2770,7 +2770,7 @@ struct mkroom *mkr;
 #else
         topologize(aroom); /* set roomno */
 #endif
-        aroom->needfill = r->filled;
+        aroom->needfill = r->needfill;
         aroom->needjoining = r->joined;
         return aroom;
     }
@@ -3831,7 +3831,8 @@ lua_State *L;
         tmproom.rtype = get_table_roomtype_opt(L, "type", OROOM);
         tmproom.chance = get_table_int_opt(L, "chance", 100);
         tmproom.rlit = get_table_int_opt(L, "lit", -1);
-        tmproom.filled = get_table_int_opt(L, "filled", g.in_mk_themerooms ? 0 : 1);
+        /* theme rooms default to unfilled */
+        tmproom.needfill = get_table_int_opt(L, "filled", g.in_mk_themerooms ? 0 : 1);
         tmproom.joined = get_table_int_opt(L, "joined", 1);
 
         if (!g.coder->failed_room[g.coder->n_subroom - 1]) {
@@ -5599,7 +5600,7 @@ genericptr_t arg;
 }
 
 /* region(selection, lit); */
-/* region({ x1=NN, y1=NN, x2=NN, y2=NN, lit=BOOL, type=ROOMTYPE, joined=BOOL, irregular=BOOL, prefilled=BOOL [ , contents = FUNCTION ] }); */
+/* region({ x1=NN, y1=NN, x2=NN, y2=NN, lit=BOOL, type=ROOMTYPE, joined=BOOL, irregular=BOOL, filled=NN [ , contents = FUNCTION ] }); */
 /* region({ region={x1,y1, x2,y2}, type="ordinary" }); */
 int
 lspo_region(L)
@@ -5607,9 +5608,9 @@ lua_State *L;
 {
     xchar dx1, dy1, dx2, dy2;
     register struct mkroom *troom;
-    boolean prefilled = FALSE, room_not_needed,
+    boolean do_arrival_room = FALSE, room_not_needed,
             irregular = FALSE, joined = TRUE;
-    int rtype = OROOM, rlit = 1;
+    int rtype = OROOM, rlit = 1, needfill = 0;
     int argc = lua_gettop(L);
 
     create_des_coder();
@@ -5617,13 +5618,12 @@ lua_State *L;
     if (argc <= 1) {
         lcheck_param_table(L);
 
-        /* TODO: check the prefilled, what was the default in lev_comp? */
-        /* "unfilled" == 0, "filled" == 1, missing = "filled" */
-
-        /* TODO: "unfilled" ==> prefilled=1 */
-        prefilled = get_table_boolean_opt(L, "prefilled", 0);
+        /* TODO: "unfilled" ==> filled=0, "filled" ==> filled=1, and
+         * "lvflags_only" ==> filled=2, probably in a get_table_needfill_opt */
+        needfill = get_table_int_opt(L, "filled", 0);
         irregular = get_table_boolean_opt(L, "irregular", 0);
         joined = get_table_boolean_opt(L, "joined", 1);
+        do_arrival_room = get_table_boolean_opt(L, "arrival_room", 0);
         rtype = get_table_roomtype_opt(L, "type", OROOM);
         rlit = get_table_int_opt(L, "lit", -1);
         dx1 = get_table_int_opt(L, "x1", -1); /* TODO: area */
@@ -5668,10 +5668,16 @@ lua_State *L;
     get_location(&dx1, &dy1, ANY_LOC, (struct mkroom *) 0);
     get_location(&dx2, &dy2, ANY_LOC, (struct mkroom *) 0);
 
-    /* for an ordinary room, `prefilled' is a flag to force
-       an actual room to be created (such rooms are used to
-       control placement of migrating monster arrivals) */
-    room_not_needed = (rtype == OROOM && !irregular && !prefilled && !g.in_mk_themerooms);
+    /* Many regions are simple, rectangular areas that just need to set lighting
+     * in an area. In that case, we don't need to do anything complicated by
+     * creating a room. The exceptions are:
+     *  - Special rooms (which usually need to be filled).
+     *  - Irregular regions (more convenient to use the room-making code).
+     *  - Themed room regions (which often have contents).
+     *  - When a room is desired to constrain the arrival of migrating monsters
+     *    (see the mon_arrive function for details).
+     */
+    room_not_needed = (rtype == OROOM && !irregular && !do_arrival_room && !g.in_mk_themerooms);
     if (room_not_needed || g.nroom >= MAXNROFROOMS) {
         region tmpregion;
         if (!room_not_needed)
@@ -5689,8 +5695,7 @@ lua_State *L;
     troom = &g.rooms[g.nroom];
 
     /* mark rooms that must be filled, but do it later */
-    if (rtype != OROOM)
-        troom->needfill = (prefilled ? 2 : 1);
+    troom->needfill = needfill;
 
     troom->needjoining = joined;
 
@@ -5711,9 +5716,6 @@ lua_State *L;
 #endif
     }
 
-    if (g.in_mk_themerooms && prefilled)
-        troom->needfill = 1;
-
     if (!room_not_needed) {
         if (g.coder->n_subroom > 1)
             impossible("region as subroom");
diff --git a/test/test_des.lua b/test/test_des.lua
index 8cb281bce..9275d801a 100644
--- a/test/test_des.lua
+++ b/test/test_des.lua
@@ -324,8 +324,8 @@ end
 function test_region()
    des.region(selection.area(08,03,54,03),"unlit")
    des.region(selection.area(56,02,60,03),"lit")
-   des.region({ region={16,05, 25,06}, lit=1, type="barracks", prefilled=0 })
-   des.region({ region={1,5, 3,7}, lit=1, irregular=true, prefilled=true, joined=false })
+   des.region({ region={16,05, 25,06}, lit=1, type="barracks", filled=0 })
+   des.region({ region={1,5, 3,7}, lit=1, irregular=true, filled=1, joined=false })
 end
 
 function test_door()