diff --git a/src/resistances.lua b/src/resistances.lua
new file mode 100644
index 0000000..ce0301c
--- /dev/null
+++ b/src/resistances.lua
@@ -0,0 +1,67 @@
+-- Elemental damage typing. Every hit that lands - melee, a bolt, a thrown
+-- weapon, a hazard tick, a status effect's damage-over-time - is tagged with
+-- one of the types below, and this module decides how much of it actually
+-- gets through. A defender's tier for a type comes from up to two places: its
+-- own base profile (bestiary data, e.g. a dragon's own hide) and whatever it
+-- has equipped (weapon/armor/ring/bow, e.g. a ring of cold resistance). The
+-- single best (most protective) tier across those sources wins - immune beats
+-- resist beats weak beats the normal default - so a found ring can cancel out
+-- an innate vulnerability, but nothing ever stacks two resists into a second
+-- discount or two weaknesses into a bigger penalty.
+
+local Resistances = {}
+
+Resistances.PHYSICAL = "physical"
+Resistances.FIRE = "fire"
+Resistances.COLD = "cold"
+Resistances.POISON = "poison"
+Resistances.LIGHTNING = "lightning"
+Resistances.ARCANE = "arcane"
+
+Resistances.TYPES = {
+  Resistances.PHYSICAL, Resistances.FIRE, Resistances.COLD,
+  Resistances.POISON, Resistances.LIGHTNING, Resistances.ARCANE,
+}
+
+Resistances.IMMUNE = "immune"
+Resistances.RESIST = "resist"
+Resistances.WEAK = "weak"
+Resistances.NORMAL = "normal"
+
+local RANK = { immune = 3, resist = 2, weak = 1, normal = 0 }
+
+-- Slots checked alongside an entity's own `resist` table, in a fixed order so
+-- the result never depends on Lua's unspecified pairs() iteration order.
+local EQUIP_SLOTS = { "weapon", "armor", "ring", "bow" }
+
+local function tierFrom(source, damageType)
+  return source and source.resist and source.resist[damageType]
+end
+
+-- The single tier that governs `damageType` incoming against `entity`, folding
+-- in its own base profile and every equipped slot that carries one.
+function Resistances.tierOf(entity, damageType)
+  local best = tierFrom(entity, damageType) or Resistances.NORMAL
+  for _, slot in ipairs(EQUIP_SLOTS) do
+    local tier = tierFrom(entity[slot], damageType)
+    if tier and RANK[tier] > RANK[best] then
+      best = tier
+    end
+  end
+  return best
+end
+
+-- Scales a already-computed `amount` of `damageType` damage by `entity`'s
+-- tier for that type. Immune drops it to nothing outright rather than merely
+-- halving it, so it can floor damage below the "always at least 1" guarantee
+-- combat.lua's own minimum otherwise enforces.
+function Resistances.apply(entity, amount, damageType)
+  if amount <= 0 then return amount end
+  local tier = Resistances.tierOf(entity, damageType or Resistances.PHYSICAL)
+  if tier == Resistances.IMMUNE then return 0 end
+  if tier == Resistances.RESIST then return math.floor(amount / 2) end
+  if tier == Resistances.WEAK then return math.floor(amount * 1.5) end
+  return amount
+end
+
+return Resistances
diff --git a/src/runewords.lua b/src/runewords.lua
new file mode 100644
index 0000000..32e91bc
--- /dev/null
+++ b/src/runewords.lua
@@ -0,0 +1,77 @@
+-- Rune stones drop as dungeon loot and slot into a weapon or armor's rune
+-- chain in the order they are socketed. A chain that exactly matches a
+-- cataloged sequence forms a runeword: a fixed, always-on stat bonus read
+-- live by combat.lua (the same additive-bonus pattern skills.lua already
+-- uses for berserk/mana shield), rather than baked permanently into the
+-- item's own power the way affixes.lua or crafting.lua's gems are - so a
+-- runeword needs no equip-time stat sync, and simply stops applying the
+-- instant a further rune breaks its exact match.
+
+local Items = require("items")
+
+local Runewords = {}
+
+Runewords.MAX_RUNES = 3
+
+Runewords.RUNES = { "sol", "ith", "tal", "ral", "eth", "amn" }
+
+-- Keyed by the chain's runes joined in slotted order - an exact match only,
+-- so a chain longer or shorter than a given word never qualifies for it.
+Runewords.WORDS = {
+  ["sol-ith"]     = { name = "Zenith",   attack = 3 },
+  ["tal-ral"]     = { name = "Bastion",  defense = 3 },
+  ["eth-amn-sol"] = { name = "Undertow", attack = 2, defense = 2 },
+}
+
+local function wordKey(runes)
+  return table.concat(runes, "-")
+end
+
+function Runewords.rune(key)
+  return { kind = Items.RUNE, rune = key, name = key .. " rune", glyph = "1" }
+end
+
+local function slottable(item)
+  return item.kind == Items.WEAPON or item.kind == Items.ARMOR
+end
+
+-- Appends `rune`'s key to `item`'s chain. Fails once the item is full or is
+-- not a weapon/armor; never fails on a rune that will not complete a known
+-- word, since an unmatched chain simply confers no bonus rather than being
+-- rejected outright - there is no wasted resource to protect against the way
+-- crafting.lua guards a gem merge against mismatched pairs.
+function Runewords.socket(item, rune)
+  if not slottable(item) then return false, "cannot hold runes" end
+  item.runes = item.runes or {}
+  if #item.runes >= Runewords.MAX_RUNES then return false, "the rune chain is full" end
+  item.runes[#item.runes + 1] = rune.rune
+  return true
+end
+
+-- The cataloged word `item`'s current chain forms, or nil if it matches none
+-- (including an empty chain, or one that no longer exactly matches any entry
+-- once it has grown past a shorter word's own length).
+function Runewords.activeWord(item)
+  if not item or not item.runes or #item.runes == 0 then return nil end
+  return Runewords.WORDS[wordKey(item.runes)]
+end
+
+function Runewords.attackBonus(entity)
+  local total = 0
+  local weaponWord = entity.weapon and Runewords.activeWord(entity.weapon)
+  if weaponWord then total = total + (weaponWord.attack or 0) end
+  local armorWord = entity.armor and Runewords.activeWord(entity.armor)
+  if armorWord then total = total + (armorWord.attack or 0) end
+  return total
+end
+
+function Runewords.defenseBonus(entity)
+  local total = 0
+  local weaponWord = entity.weapon and Runewords.activeWord(entity.weapon)
+  if weaponWord then total = total + (weaponWord.defense or 0) end
+  local armorWord = entity.armor and Runewords.activeWord(entity.armor)
+  if armorWord then total = total + (armorWord.defense or 0) end
+  return total
+end
+
+return Runewords