Siege Weapons

Variant Rules

Siege engines are the great equalizers of fantasy warfare — tools that let even small forces threaten mighty fortifications, and that transform battles from skirmishes into legendary encounters. Whether PCs are defending a lonely outpost or leading the assault on a tyrant's castle, these rules cover the full range of ranged bombardment, fire-spewing artillery, and close assault machinery.

Optional Rule. These rules supplement and expand the siege engine rules in the Core Rulebook. Where they conflict, use the rules below. All siege engines are at least size Large and use the following universal rules unless their description states otherwise.

Siege Engine Qualities

Every siege engine stat block uses the following column headers. Learn these once and every table on this page becomes immediately readable.

StatMeaning
Cost Price in gp, including operating gear and upkeep equipment. Ammunition listed separately.
Dmg Damage dealt on a hit. "See description" means the engine has a special attack mode (area, line, cone). No sneak attack or precision damage applies.
Critical Critical threat range and multiplier. Siege engines can critically damage objects as well as creatures. "—" means no critical is possible.
Range First range increment. Each full increment beyond it adds a cumulative –2 to the attack or targeting check. Minimum ranges shown as "(X ft. min.)" — the engine cannot target closer.
Type B = Bludgeoning, P = Piercing, S = Slashing. "B and P" means both types simultaneously. Energy engines list the energy type instead.
StatMeaning
Crew Minimum number of Medium creatures needed. Assumes Medium crew. Small creatures require double; each Large creature counts as 4, Huge as 8, Colossal as 16, Gargantuan as 20.
Aim Full-round actions required to aim. Halved to move actions with the Master Siege Engineer feat. Reduced crew doubles this number.
Load Full-round actions required to load ammunition. Halved to move actions with the Master Siege Engineer feat.
Speed Distance moved when the full crew takes a move action to push it. Speed 0 means the engine must be disassembled before transport (or mounted on a vehicle).

Siege Engine Rules

Siege engines are exotic weapons. The Siege Engineer feat grants proficiency with all siege engines, including siege firearms. Proficiency with firearms also grants proficiency with siege firearms, but not other siege engines.

One crew member is the crew leader, who aims, fires, and makes checks. The rest load, push, and assist. Crew counts assume Medium creatures.

Creature SizeCounts As
Small½ crew member (double crew required)
Medium1 crew member
Large4 crew members
Huge8 crew members
Gargantuan20 crew members
Colossal16 crew members

A siege engine can be masterwork (Craft DC +5, +300 gp). A masterwork siege engine can be magically enchanted at twice the normal cost for a weapon.

The enhancement bonus applies on attack rolls and targeting checks. For magical spell engines (firedrake, firewyrm), it also applies on damage rolls.

Siege engines are objects with Dex 0 (–5) plus a size penalty. Each engine type has its own hardness and hit points listed in its description.

Siege engines can be armored. Treat the engine as a creature of its size to determine armor cost. Masterwork siege engine armor can be enchanted at twice normal cost. Armored engines gain the armor's AC bonus, use the armor's hardness and hit points, and gain bonus hit points equal to the armor bonus × 5.

The Speed entry shows how far the engine moves when the full crew takes a move action. Speed 0 means the engine must be disassembled before transport — or mounted on a vehicle (see Vehicle rules). Siege engines atop or mounted on vehicles move with those vehicles.

Unlike normal ranged weapons, siege engines do not deal half damage when attacking objects. They are purpose-built to break walls, gates, and fortifications.

  • Direct-fire and close assault engines confirm criticals normally.
  • Indirect-fire engines can score a critical on a natural 20 targeting check — the crew leader must reroll to confirm; if confirmed, multiply damage by the critical multiplier.
  • Siege engine criticals can damage objects — unlike normal weapon criticals.
  • Siege engines do not benefit from critical feats the crew or crew leader possess.

Non-Firearm Siege Engines

A natural 1 on an attack roll or targeting check causes a mishap, applying the broken condition: –2 on attack rolls, targeting checks, and damage rolls; speed halved. A crew leader with the Siege Engineer feat does not trigger mishaps on a natural 1.

Firearm Siege Engines

  • Firearm siege engines have a misfire range (listed per engine). Any roll within the misfire range misses and applies the broken condition.
  • Broken firearm siege engines have misfire range +4.
  • A broken firearm siege engine that misfires explodes — dealing its damage to all creatures within the listed blast radius (DC 20 Reflex halves).
  • The Siege Engineer feat does not reduce misfire values for firearm siege engines.

Building or repairing a siege engine requires a DC 20 Craft (siege engine) check. This applies whether you are building from scratch or restoring a damaged engine.

A siege engine is a difficult device: disabling it requires 2d4 rounds and a DC 20 Disable Device check.

A disabled engine either stops working immediately or malfunctions 1d4 minutes after use (sabotage). Fixing a disabled engine: DC 20 Craft (siege engine), Disable Device, or Knowledge (engineering); takes 10 minutes; can retry on failure.

Siege engines are transported broken down and assembled on-site. Each worker must succeed at a DC 10 Craft (siege engine) check (untrained workers may not take 10). Using half the required workers doubles the time; fewer than half and assembly is impossible.

Assembly Requirements by Engine Size
Engine SizeTime RequiredWorkers Required
Small1 minute1
Medium10 minutes2
Large1 hour4
Huge2 hours6
Gargantuan4 hours8
Colossal8 hours12

Fire Modes: Direct vs. Indirect

Direct Fire flat trajectory

Uses a normal attack roll. Can target creatures or barriers directly in front of the engine.

  • –2 attack roll penalty per size category the engine is larger than the aimer.
  • Knowledge (engineering) ranks or a targeting platform eliminates the size penalty.
  • Each extra crew member (no smaller than 3 size categories below the engine) reduces the size penalty by 2.
  • Nonproficiency penalty applies normally.
Indirect Fire arcing trajectory

Uses a targeting check (not an attack roll) against a target square. Can arc over walls and fortifications.

  • Targeting check = BAB + Int mod (or Knowledge [engineering] if trained) + proficiency penalty.
  • Natural 1 triggers a mishap (broken condition).
  • Natural 20 can score a critical hit (crew leader must confirm).
  • Minimum range applies — cannot target squares closer than the listed minimum.

Indirect Attack: When You Miss

If the targeting check fails, the shot scatters:

  1. Roll 1d8 for direction. 1 = falls short (toward the engine). 2–8 count clockwise around the target square.
  2. Roll 1d4 per range increment between the engine and target. The total is the number of squares the shot travels in the rolled direction.

The ammunition deals its damage in the square it lands on.

Indirect Attack Check Modifiers
ConditionModifier
No line of sight to target square –6
Successive shots — crew can see where last miss landed Cumulative +2/miss (max +10)
Successive shots — observer providing feedback only Cumulative +1/miss (max +5)
Successive shots after a hit +10

Weapon Catalog

Aim and Load values are in full-round actions (reduced to move actions with the Master Siege Engineer feat). Reduced crew doubles Aim time.

EngineCostDmgCritical RangeTypeCrewAimLoadSpeed
Direct-Fire — Large
Ballista, light500 gp3d819–20/×2120 ft.P10210 ft.
Cannon6,000 gp6d6×4100 ft.B&P21310 ft.
Direct-Fire — Huge
Ballista, heavy800 gp4d819–20/×2180 ft.P3230 ft.
Cannon, fiend's mouth9,000 gp8d6×4150 ft.B&P3130 ft.
Firedrake4,000 gp6d6——fire32510 ft.
Direct-Fire — Gargantuan
Ballista, gate breaker1,200 gp6d819–20/×2100 ft.B5350 ft.
Firewyrm6,000 gp6d6——fire5260 ft.
Indirect-Fire — Large
Bombard, light6,000 gp5d6×4100 ft. (50 min.)B&P21310 ft.
Catapult, light550 gp4d6×2150 ft. (50 min.)B22310 ft.
Trebuchet, light800 gp4d6×2200 ft. (100 min.)B3230 ft.
Indirect-Fire — Huge
Bombard, standard8,000 gp7d6×4150 ft. (100 min.)B&P2130 ft.
Catapult, standard800 gp6d6×2200 ft. (100 min.)B3230 ft.
Springal, arrow1,000 gp3d8×3100 ft. (50 min.)P3230 ft.
Springal, rocket6,000 gp3d10×4100 ft. (50 min.)fire3230 ft.
Trebuchet, standard1,000 gp6d6×2300 ft. (150 min.)B4230 ft.
Indirect-Fire — Gargantuan
Bombard, heavy16,000 gp9d6×4200 ft. (100 min.)B&P4350 ft.
Catapult, heavy1,000 gp8d6×2300 ft. (100 min.)B4330 ft.
Trebuchet, heavy1,500 gp8d6×2400 ft. (200 min.)B4330 ft.

Range entries showing "(X min.)" indicate the minimum range — the engine cannot target closer than that distance.

Resembles a massive crossbow powered by twisted sinew torsion springs. A cord attached to both arms is winched back and a bolt loaded into a grooved slider. All ballistae are direct-fire weapons.

  • Light (Large): The workhorse ballista — often called an arbalest or scorpion. Maneuverable; fits atop towers or vehicles. Hardness 5, 50 hp. Bolts: 10 gp, 10 lbs. each.
  • Heavy (Huge): Standard castle and warship defense. Hardness 5, 100 hp. Bolts: 30 gp, 20 lbs. each.
  • Gate Breaker (Gargantuan): Fires blunt-tipped weighted quarrels as a long-range battering ram. Deals full damage to wooden structures on a hit; deals its damage to a 10-ft. square rather than a single target.

Cauldron-shaped or cannon-shaped firearms that lob payloads in an arc — normally indirect-fire, but can be direct-fired at a –4 attack penalty with range increment halved. All bombards are siege firearms with a misfire range.

  • Light (Large): Targeting DC 15. Often swivel-mounted into ground or castle walls to manage recoil.
  • Standard (Huge): Targeting DC 20. Greatest variety of forms; may include stabilizing mechanisms for recoil management.
  • Heavy (Gargantuan): Targeting DC 25. Often fixed to hilltops or massive keeps. Frequently built in two pieces joined by a screw mechanism.

Metal siege firearms — cast in one piece or welded with iron bands — using black powder to propel solid shot at great force. Direct-fire weapons.

  • Cannon (Large): Misfire range 1 (20 ft. blast on explosion). Hardness 10, 70 hp. Cannonballs: 30 gp, 25 lbs. each.
  • Fiend's Mouth Cannon (Huge): Usually built in multiple pieces, often shaped with a fiend's head at the muzzle. Misfire range 1 (30 ft. blast). Hardness 10, 140 hp. Balls: 45 gp, 40 lbs. each.

Winched torsion arm with a payload cup. Indirect-fire. Can hurl standard stones or special ammunition.

  • Light (Large): Targeting DC 15. Wheeled. Hardness 5, 50 hp. Stones: 10 gp, 50 lbs. each.
  • Standard (Huge): Targeting DC 20. Too large for one-piece transport — requires assembly. Stones: 15 gp, 75 lbs. each.
  • Heavy (Gargantuan): Targeting DC 25. Requires assembly. Stones: 20 gp, 100 lbs. each.

Alchemical fire-spewing siege engines. Not traditional projectile weapons — they spray fire in lines or cones. No critical hits possible.

  • Firedrake (Huge): Wheeled or vehicle-mounted. Fires a 60-ft. line or 30-ft. cone (crew leader's choice). 6d6 fire damage, DC 15 Reflex halves; failed save also catches fire.
  • Firewyrm (Gargantuan): Larger firedrake requiring assembly. 120-ft. line or 60-ft. cone. 6d6 fire damage, DC 20 Reflex halves.

Uses a torsion-cranked paddle to strike a firing rack, launching multiple projectiles in an arc. Indirect-fire; attacks affect a 15-ft. burst centered on the target square.

  • Arrow Springal: Rains arrows on target and 15-ft. burst. Ammunition: 20 gp, 10 lbs. per use.
  • Rocket Springal: Highly volatile black-powder rockets. If it misfires, it explodes — dealing its damage to all creatures within 20 ft. (no save). Ammunition: 250 gp, 20 lbs. per use.

Counterweight-arm indirect-fire engines. On a hit, trebuchet ammunition scatters — full damage to the target square, half damage to adjacent squares (radius based on trebuchet size).

  • Light (Large): Targeting DC 15. Scatters to adjacent squares (5 ft.).
  • Standard (Huge): Targeting DC 20. Requires assembly. Scatters to 10 ft. radius.
  • Heavy (Gargantuan): Targeting DC 25. Requires assembly. Scatters to 15 ft. radius. Stones: 30 gp, 200 lbs. each.

Close assault engines are used at the walls — to bridge gaps, bypass defenses, batter through gates, or deliver soldiers safely to the ramparts. Most deal no direct damage but serve essential assault roles.

EngineCostDmgCritical TypeCrewSpeed
Assault Bridge
  Large1 gp—————
  Huge10 gp—————
  Gargantuan50 gp—————
  Colossal250 gp—————
Corvus
  —100 gp———1Special
Gallery
  Large250 gp———315 ft.
  Huge500 gp———615 ft.
  Gargantuan1,000 gp———915 ft.
  Colossal2,000 gp———1815 ft.
Escalade Ladder
  Large5 gp———2as crew
  Huge10 gp———4as crew
  Gargantuan50 gp———6as crew
  Colossal250 gp———8as crew
Ram
  Large500 gp2d6×3B515 ft.
  Huge1,000 gp3d6×3B1015 ft.
  Gargantuan2,000 gp6d6×3B2015 ft.
  Colossal5,000 gp10d6×3B4015 ft.
Siege Tower
  Large1,000 gp———615 ft.
  Huge2,000 gp———1215 ft.
  Gargantuan5,000 gp———2415 ft.
  Colossal10,000 gp———4815 ft.

Spans ditches, moats, or gaps. Raising takes 1 full-round action per 5 feet of length; up to 4 creatures can cooperate to raise it together. Time doubles in difficult terrain.

SizeWidthLength/Height
Large5 ft.20 ft.
Huge5 ft.30 ft.
Gargantuan10 ft.40 ft.
Colossal10 ft.60 ft.

A boarding device: a hinged bridge mounted vertically on a siege tower or vehicle, with a hooked end to grab onto a target structure or vehicle. Typically 10 ft. wide and up to 30 ft. long. Dropping the corvus onto a target is a standard action for the crew leader; a hooked corvus can be cleared with a DC 25 Strength check (full-round action for up to 4 creatures).

A mobile temporary cover structure of hide or wood, used to protect assault crews from ranged fire as they advance. Flimsy galleries provide cover; stouter examples can be given siege engine armor (adjust AC, hardness, and hp accordingly). A gallery can carry a gallery ram internally — the ram then does not require a charge action for full momentum.

Spiked base for stability. The upper 5 ft. are metal-shod (hardness 10, 20 hp); the remainder is wooden (hardness 5, hp by size). Large ladders have 75 hp; Huge have 150 hp; Gargantuan have 600 hp; Colossal have 2,400 hp.

Iron-shod logs carried by the crew. Can deal damage or make a Strength check against a target's break DC. Hardness 5; Large 30 hp, Huge 120 hp, Gargantuan 320 hp, Colossal 1,280 hp.

  • Charge required: All crew must charge to get full effect; non-chargers can still assist but the crew leader makes the roll.
  • Damage attack: Crew leader rolls attack (–4 nonproficiency) + Str mods of leader and all assisting crew.
  • Break check: Crew leader makes Strength check (+2 bonus), +2 per assisting crew member.
  • Improvised ram: Any log works at –4 on attacks, damage, and Strength checks.
  • Pick head: +2 circumstance on checks and rolls vs. stone structures.
  • Screw head: +2 circumstance on checks and rolls vs. earthen structures.
  • Gallery ram: Suspended from a gallery — no charge action required; can add tethers to increase crew size.

A stout wooden gallery with multiple stories and a roof section. The lower story houses the propulsion crew (total cover). Upper stories carry soldiers who can attack from cover or deploy a corvus from the roof.

Siege Tower Soldier Capacity
SizeMax Soldiers Carried
Large5
Huge20
Gargantuan40
Colossal100

Special ammunition can be loaded into select indirect-fire siege engines or cannons. Compatible engine types are noted in each description. Costs and weights are per use.

AmmunitionCostWeight
Alchemist's fire200 gp10 lbs.
Blast shot30 gp25 lbs.
Bomb600 gp30 lbs.
Chain shot50 gp30 lbs.
Liquid ice400 gp20 lbs.
Plague bundle80 gp20 lbs.
Smoke shot250 gp20 lbs.

A ceramic canister for catapults and trebuchets. On impact: 4d6 fire damage to each creature and wooden structure within 5 ft. of the target square (DC 20 Reflex halves). Creatures that fail their save catch fire.

A bundle of pellets, balls, or scrap metal for cannons and fiend's mouth cannons. Instead of single-target damage, blast shot deals the engine's damage in a 30-ft. cone (DC 20 Reflex halves). At close range (within first range increment) the cone extends to 60 ft.

A metal canister of metal balls and black powder for catapults and trebuchets (or carried by 2 Medium / 1 Large creature). Explodes on impact or with a 1-second fuse: deals 6d6 piercing and bludgeoning damage in a 10-ft. radius (DC 20 Reflex halves). Can be set to explode on impact or with a short delay.

For cannons and fiend's mouth cannons. Especially effective against sails and dirigibles — deals double normal damage to those vehicle propulsion components. Against other targets it deals normal cannon damage.

A ceramic canister for catapults and trebuchets. On impact: 4d6 cold damage to each creature within 5 ft. of the target square (DC 20 Reflex halves). Creates a 10-ft.-radius patch of ice that is treated as difficult terrain for 2d4 rounds.

A ceramic canister of diseased carrion for catapults and trebuchets. Deals only half normal damage, but every creature hit is exposed to filth fever (DC 12, onset 1d3 days, 1d3 Dex / 1d3 Con). Used for long-duration siege harassment.

A ceramic sphere with two separated alchemical substances (similar to a smoke pellet) for catapults and trebuchets. Deals 2d6 damage on impact, then creates a 20-ft.-radius smoke cloud for 1d4+4 rounds (as obscuring mist). The cloud can be dispersed by moderate wind in 4 rounds or strong wind in 1 round.

Structure Hardness & Hit Points

The primary targets of siege engines. When any structure gains the broken condition, its hardness is halved. A building reduced to half hit points is broken (accessible but standing); at 0 hp it collapses (creatures inside suffer a cave-in). A wall square must be reduced to 0 hp to breach it; a gate becomes breached (passable as one size smaller) when it gains the broken condition.

Buildings

AC: Large 4 · Huge 3 · Gargantuan+ 0. Flimsy buildings have half listed hp. Magically treated: double hardness and hp.

MaterialHard.Hit Points by Size
LargeHugeGargan.Colossal
Wood51202709603,240
Stone82004501,6005,400
Iron/Steel104009003,20010,800
Adamantine205601,2604,48015,120

Gates

AC: Large 4 · Huge 3 · Gargantuan+ 0. Broken condition = breached (passable as one size smaller). Magically treated: double hardness and hp.

MaterialBreak DC1Hard.Hit Points by Size
LgHugeGar.Col.
Wood35560135240540
Stone388100225400900
Iron/Steel24102005008001,800
Adamantine48202806301,1202,520
1 Assumes Large, barred and locked. Huge +5, Colossal +10, Gargantuan +15. Arcane lock +10.

Walls

AC 5 per 5-ft. square. Broken condition halves hardness but doesn't breach. Only reducing a square to 0 hp breaches it; sections above then fall (reduced to half current hp – 1). Magically treated: double hardness and hp (500 gp per square).

MaterialHardnessHP per 5-ft. sq.
Wood560
Masonry890
Superior masonry8180
Reinforced masonry8270
Hewn stone8540
Iron/Steel10180
Adamantine201,260
Variant Integration: Siege engines can appear in Performance Combat scenarios using the Toward a Goal format — where the objective is to breach a gate or destroy a fortification before the crowd loses interest. Indirect-fire engines aiming at fortification squares are treated as attacking objects; their performance combat check trigger fires when they land a hit on a defended structure in view of the crowd.