diff --git a/src/monsters.lua b/src/monsters.lua
new file mode 100644
index 0000000..b6c9a7f
--- /dev/null
+++ b/src/monsters.lua
@@ -0,0 +1,52 @@
+-- Data-driven bestiary. Each species is a plain table describing stats, the AI
+-- behaviour tag that governs its turn, how fast it acts, and the shallowest depth
+-- it appears at. The factory stamps a species into an Entity, scaling hp with
+-- depth so lower floors bite harder.
+
+local Entity = require("entity")
+
+local Monsters = {}
+
+Monsters.species = {
+  { key = "rat",     glyph = "r", name = "rat",            hp = 4,  attack = 2, defense = 0, speed = 110, ai = "chase",   minDepth = 1 },
+  { key = "bat",     glyph = "v", name = "cave bat",       hp = 3,  attack = 2, defense = 0, speed = 150, ai = "erratic", minDepth = 1 },
+  { key = "kobold",  glyph = "k", name = "kobold",         hp = 6,  attack = 3, defense = 1, speed = 100, ai = "pack",    minDepth = 1 },
+  { key = "goblin",  glyph = "g", name = "goblin",         hp = 5,  attack = 3, defense = 0, speed = 110, ai = "pack",    minDepth = 2 },
+  { key = "archer",  glyph = "a", name = "skeleton archer", hp = 6, attack = 3, defense = 1, speed = 100, ai = "ranged",  minDepth = 2, range = 5 },
+  { key = "orc",     glyph = "o", name = "orc",            hp = 10, attack = 4, defense = 1, speed = 100, ai = "chase",   minDepth = 3 },
+  { key = "wretch",  glyph = "w", name = "cave wretch",    hp = 8,  attack = 2, defense = 0, speed = 120, ai = "flee",    minDepth = 3 },
+  { key = "troll",   glyph = "T", name = "troll",          hp = 16, attack = 6, defense = 2, speed = 80,  ai = "chase",   minDepth = 4 },
+  { key = "mage",    glyph = "m", name = "dark mage",      hp = 8,  attack = 2, defense = 0, speed = 100, ai = "ranged",  minDepth = 5, range = 6 },
+  { key = "dragon",  glyph = "D", name = "young dragon",   hp = 30, attack = 8, defense = 3, speed = 90,  ai = "ranged",  minDepth = 6, range = 4 },
+}
+
+Monsters.byKey = {}
+for _, spec in ipairs(Monsters.species) do
+  Monsters.byKey[spec.key] = spec
+end
+
+-- Species eligible at a depth, in registry order so callers pick deterministically.
+function Monsters.forDepth(depth)
+  local eligible = {}
+  for _, spec in ipairs(Monsters.species) do
+    if spec.minDepth <= depth then
+      eligible[#eligible + 1] = spec
+    end
+  end
+  return eligible
+end
+
+function Monsters.create(spec, id, x, y, depth)
+  local bonusHp = depth - 1
+  return Entity.new({
+    id = id,
+    x = x, y = y,
+    glyph = spec.glyph, name = spec.name, kind = "monster",
+    species = spec.key, ai = spec.ai,
+    hp = spec.hp + bonusHp, maxHp = spec.hp + bonusHp,
+    attack = spec.attack, defense = spec.defense,
+    speed = spec.speed, range = spec.range or 0,
+  })
+end
+
+return Monsters