Cannon Golem — The Iron Thunderer
A fortress that thought itself safe behind its walls is not safe from the Iron Thunderer.
Six bells ring from the eastern watchtower. The seventh is lost beneath the concussion of an enormous gun. A jagged figure advances through smoke from an abandoned siege work. The cannon fitted in its arm turns towards the gate. No officer is directing it; the last commander died a century ago.
A cannon golem is an extraordinarily rare weapon of golemcraft: a twelve-foot construct of brass, cold iron, enchanted alloys and bound motive force, built to move artillery where no wheeled carriage can pass. Most bear a cannon in one arm and a crushing hammer-fist in the other. Their interior chambers hold powder and mechanical feeding gear, while arcane pockets maintain the delicate explosive mixture that keeps the weapon firing.
It does not hunt for sport, choose political causes or fear death. It follows an old definition of friend, foe, or forbidden ground, sometimes with murderous consequences when the banners have changed.
The Forgotten Cannon
Long after the earliest dwarven ward-smiths fashioned guardians for refuge gates and clan archives, specialist armourers began to ask whether a golem could guard an entire road rather than a single door. The answer was a cannon golem, heavy and expensive enough that only the richest strongholds could afford one. Some used gunpowder worked by ingenious mechanical chambers; others joined the art of black-powder weapons to arcane bindings which supply powder without need of carts or exposed magazines.
The cannon golem is an exception, not proof that every army fields enchanted artillery. Found only in a handful of guild war-vaults, mountain fortresses and remote military laboratories, it is often the one surviving weapon of an abandoned campaign. Its orders may refer to a bridge no longer standing, the colours of a vanished regiment, or a charter whose rightful successor is disputed.
What Is Happening Right Now?
A gunwork concealed in the mountains has reopened its western breach. Each dawn the golem walks to the same range marker and fires into a deserted valley. The iron shot is beginning to fall among newly built cottages beyond the ridge. The present lord insists the weapon belongs to him; a dwarven guild produces an older contract forbidding the machine from serving any noble household. A surviving command plate bears a third name, erased and replaced with fresh brass.
The adventurers can retrieve the plate, discover who has been resetting the range, redirect the cannon away from the settlements or bring competing claimants before the old ward-smith’s heirs. Destroying it would spare the valley but deprive the fortress of its only workable defence against an approaching army.
Appearance, Habits and Orders
Its face resembles the visor of an executioner’s helm, though no eyes are needed inside the metal. A drum of shot rattles in a shoulder socket; narrow vents bleed heat after firing. Some are almost statuesque until activated. Others patrol with deliberate, ponderous steps, turning their cannon arm before the body follows.
The machine is not a tactician. A binding can make it shoot intruders on a rampart, advance along an approach road or defend a warehouse, but it cannot discover that a new peace treaty has invalidated the old order. Clever adversaries can exploit the exact boundaries of its patrol. Equally, a mistaken signal can send its cannonade into the people it was sworn to shelter.
Cannon Golem Stat Blocks
Choose your game’s edition. The Pathfinder 1e and third-party 2014-compatible blocks use published rules; the 2024 and 3.5e versions are explicitly labelled conversions. Never combine weapon reloads, critical multipliers or cannonade rules from different tabs.
Cannon Golem — D&D 2024
Original campaign conversion · Large Construct, Unaligned · CR 16 (15,000 XP; PB +5)
AC 20 (layered alloy armour); Initiative +4 (14); HP 252 (24d10 + 120); Speed 30 ft.
| STR | DEX | CON | INT | WIS | CHA |
|---|---|---|---|---|---|
| 24 (+7) | 9 (−1) | 20 (+5) | 3 (−4) | 11 (+0) | 1 (−5) |
Saving Throws Con +10, Wis +5. Damage Immunities Fire, Poison, Psychic; Condition Immunities Charmed, Exhaustion, Frightened, Paralyzed, Petrified, Poisoned.
Senses Darkvision 120 ft., Passive Perception 10. Languages Understands the maker’s languages but cannot speak.
Traits
Fire Absorption. If the golem would take Fire damage, it instead regains that many Hit Points. If an effect would deal at least 20 Fire damage at once, its cannon may backfire: DC 18 Constitution save or the golem takes 18 (4d8) Force damage and cannot fire its cannon until the end of its next turn. This self-damage bypasses its immunities.
Immutable Form. The golem cannot shape-shift. Magic Resistance. Advantage on saves against spells and other magical effects.
Siege Construction. Its cannon and cannonade deal double damage to objects and structures.
Actions
Multiattack. Three attacks in any combination of Fist and Cannon, but no more than two Cannon attacks.
Fist. Melee Attack Roll +12, reach 10 ft., one target. Hit: 20 (3d8 + 7) Bludgeoning damage. If the target is Large or smaller, it makes a DC 20 Strength save or falls Prone.
Cannon. Ranged Attack Roll +12, range 100/400 ft., one target. Hit: 29 (4d10 + 7) Bludgeoning damage. The golem uses its Strength modifier through a rune-guided aiming assembly.
Cannonade (Recharge 5–6). The golem fires a shattering burst in a 60-foot line 10 feet wide. Creatures in the line make a DC 18 Dexterity save, taking 54 (12d8) Bludgeoning damage on failure or half on success. Objects and structures in the line take double damage.
Reaction
Point-Blank Defence. When a creature within 10 feet hits the golem with a melee attack, it may make one Fist attack against that creature if the attacker is still in reach.
Battlefield Use
At close range three Fists average 60 damage on three hits. With two Cannons and one Fist, the golem averages 78 on three hits; its cannonade punishes clustered enemies but replaces its attacks for that action. Cover, ammunition-supply seals and the command tablet offer tactical counterplay.
Homebrew rules for 2024 play, not an official D&D 2024 stat block; inspired by Pathfinder Bestiary 3 and Legendary Games’ 5e Cannon Golem.
Cannon Golem — Pathfinder 1e
Published Pathfinder 1e (Bestiary 3) · CR 15 (51,200 XP) · N Large Construct
Initiative +7; Senses Darkvision 60 ft., low-light vision; Perception +2.
Defence
AC 31, touch 16, flat-footed 24 (−1 size, +7 Dex, +15 natural); HP 140 (20d10 + 30); Fort +6, Ref +13, Will +8; DR 15/adamantine; Immune Construct traits and magic (exceptions below).
Offence
Speed 30 ft.; Melee 2 Slams +29 (2d10 + 10); Ranged Cannon +26/+21 (6d6 + 7; critical 19–20/×4); Space/Reach 10 ft./10 ft.
| STR | DEX | CON | INT | WIS | CHA |
|---|---|---|---|---|---|
| 30 (+10) | 24 (+7) | — | — | 15 (+2) | 2 (−4) |
Base Atk +20; CMB +31; CMD 48. Feats Improved Critical (cannon) as a bonus feat. Environment any land; Organization solitary or pair; Treasure none.
Special Abilities
Alloyed (Ex). Slam and cannon count as adamantine, cold iron and silver when overcoming damage reduction.
Cannon (Ex). Range increment 100 ft.; projectile deals 6d6 Bludgeoning and Piercing damage, with ×4 critical multiplier. The magazine holds twenty cannonballs. Adding one ball to the magazine takes a standard action, while chambering a ball to fire takes a swift action. The mechanism allows two shots in a round when ammunition is available.
Gun Training (Ex). Add the golem’s Dexterity modifier (+7) to Cannon damage.
Blasting Critical (Ex). When it confirms a critical Slam, it may fire one loaded Cannon attack at the same target as a free action.
Immunity to Magic (Ex). Immune to spells or spell-like abilities that allow spell resistance, with special exceptions. A spell with the water descriptor that affects it disables the Cannon for one round, no save; heat metal causes a backfire for 6d6 damage and Staggers it for one round, no save.
Construction
2,000 lb. of adamantine, brass, cold iron and mithral worth 10,000 gp. CL 17th; Price 200,000 gp; Cost 105,000 gp. Requires Craft Construct, geas/quest, limited wish, and plane shift or secret chest; creator CL 17th; Craft (siege engine) and Knowledge (engineering) DC 25.
Published rules: Pathfinder 1e Bestiary 3 — Cannon Golem, OGL. This edition uses actual cannonballs and a finite twenty-shot magazine.
Cannon Golem — D&D 3.5e
Original D&D 3.5e conversion · CR 15 · N Large Construct
Hit Dice 20d10 + 30 (140 HP); Initiative +7; Speed 30 ft. (6 squares).
AC 31 (−1 size, +7 Dex, +15 natural); Touch 16; Flat-footed 24; DR 15/adamantine; immune to construct traits and most magic; Darkvision 60 ft.; low-light vision.
Base Atk/Grapple +15/+29. Attack Slam +24 melee (2d10 + 10) or Cannon +21 ranged (6d6 + 7; critical 19–20/×4). Full Attack two Slams +24 melee or Cannon +21/+16 ranged. Space/Reach 10 ft./10 ft.
| STR | DEX | CON | INT | WIS | CHA |
|---|---|---|---|---|---|
| 30 (+10) | 24 (+7) | — | — | 15 (+2) | 2 (−4) |
Saves Fort +6, Ref +13, Will +8; Skills —; Bonus Feat Improved Critical (cannon). Organisation solitary or pair; Environment any land; Treasure none; Alignment always neutral.
Special Abilities
Cannon (Ex). Range increment 100 ft., standard ranged attacks, 6d6 Bludgeoning and Piercing +7 from Gun Training, and ×4 critical damage. The magazine holds twenty balls; a standard action loads one into the magazine, and a swift action chambers it for firing. The golem can fire twice in a full attack while loaded.
Alloyed (Ex). Fists and cannon count as adamantine, cold iron and silver for damage reduction. Blasting Critical (Ex). On a confirmed Slam critical hit, it may fire one loaded cannonball at that target as a free action.
Immunity to Magic (Ex). Most spells allowing spell resistance have no effect. A water-descriptor spell that affects it silences its cannon for one round. Heat metal makes the cannon backfire for 6d6 damage and Staggers the golem for one round (no saves).
Construction — Conversion Guidance
2,000 lb. of worked adamantine, brass, cold iron and mithral. Suggested CL 17th, Price 200,000 gp, material and magical cost 105,000 gp + 7,600 XP, subject to the GM’s 3.5e crafting adjustments. Suggested requirements: Craft Construct, geas/quest, limited wish, plane shift or secret chest, a creator of level 17 or higher, and Craft (siege engines) and Knowledge (engineering) DC 25.
This is a 3.5e adaptation of Paizo’s Pathfinder Cannon Golem, not a published D&D 3.5e monster. Its attack bonuses use 3.5e Construct base attack progression (BAB +15), not Pathfinder’s +20.
Cannon Golem — D&D 2014
Published third-party 5e (2014-compatible) · Legendary Games · Large Construct, Unaligned · CR 16 (15,000 XP)
AC 20 (natural armour); HP 210 (20d10 + 100); Speed 30 ft.
| STR | DEX | CON | INT | WIS | CHA |
|---|---|---|---|---|---|
| 24 (+7) | 9 (−1) | 20 (+5) | 3 (−4) | 11 (+0) | 1 (−5) |
Damage Immunities Fire, Poison, Psychic; Bludgeoning, Piercing, and Slashing from nonmagical attacks unless made with adamantine. Condition Immunities Charmed, Exhaustion, Frightened, Paralyzed, Petrified, Poisoned.
Senses Darkvision 120 ft.; Passive Perception 10. Languages Understands its creator’s languages but cannot speak.
Traits
Fire Absorption. Fire instead restores the same number of hit points. After a failed save against a fire spell dealing at least 20 damage, the golem makes a second Constitution save against that spell’s DC; on failure its cannon backfires for 6d6 damage (bypassing its immunities).
Immutable Form. Immune to effects changing its form. Magic Resistance. Advantage on saves against spells and other magical effects. Magic Weapons. Weapon attacks count as magical.
Actions
Multiattack. Two Fists, or one Fist and one Cannon attack.
Fist. Melee Weapon Attack +13, reach 5 ft., one target; hit 20 (3d8 + 7) Bludgeoning damage.
Cannon. Ranged Weapon Attack +13, range 80/320 ft.; hit 33 (4d12 + 7) Bludgeoning damage. After a hit, the golem may use a bonus action to attempt a Strength (Athletics) shove against the target, with advantage if the target is Medium or smaller.
Cannonade (Recharge 6). Blast along a 60-foot line or through a 15-foot cone. Each creature in its area makes a DC 19 Dexterity save, taking 45 (10d8) Bludgeoning damage on a failure or half on success.
Triggered Cannon Punch
On a critical hit with Fist, the golem can make a Cannon attack against that same target, provided it has not fired its Cannon or used Cannonade that turn. The original publisher lists this under Reactions but describes a bonus-action trigger; adjudicate it as a bonus action during the golem’s own turn rather than awarding an extra attack on another creature’s turn.
Based on Cannon Golem, Sea Monsters (5E) © 2021 Legendary Games (third-party OGL material). This is not an official Wizards of the Coast or D&D SRD creature.
Facing the Iron Thunderer
In a cramped vault, a cannon golem is a terrifying brawler. On open ground it is a gun platform whose shots can outrange ordinary thrown weapons. Give the players meaningful options: masonry that provides cover, a switchback road that blocks a firing line, a ventilation sluice, an ammunition magazine they can seal, or a maker’s signature hidden in a wall tablet.
Do not treat the creature’s size as an excuse for unlimited fire. In Pathfinder and the 3.5e adaptation the magazine holds twenty cannonballs, and the loading mechanism matters. In 2024 and 2014-compatible rules, follow the actions in those tabs rather than importing Pathfinder’s 19–20/×4 critical hit.
Adventure Encounters
The Gun That Still Salutes
Every sixth night a cannon fires three rounds across a treaty line. The shots have never struck the enemy town—until a landslip changes the trajectory. To stop it, the party must enter the old battery, identify the lost command word and decide which of two descendants can lawfully inherit the siege machine. Simply silencing the gun may be seen as a breach of the original peace.
Powder in the Quarry
A dwarven mining guild has uncovered an entombed cannon golem inside a sealed quarry. It recognises miners by their old sigils, but attacks any wagon bearing the new guild mark. The mine’s owners need it moved before blasting continues. The party can forge a legitimate transfer, find its original maker or lure it into the abandoned ammunition tunnel—where a collapsing ceiling would seal valuable ore forever.
A Town Behind the Gate
A noble offers an enormous reward to recover the iron guardian from a besieged castle. He intends to turn it on the attackers, but the command plate orders it to protect the gate from all armies, including his own relieving troops. The garrison’s commander is ready to destroy it. The adventurers must choose between preserving a priceless guardian and saving soldiers who never agreed to serve its ancient oath.
After the Battle
Iron shot is worth little next to an intact command gear, siege-gunner’s manual, enchanted rangefinder or golem manual bearing half-forgotten construction rites. Returning a cannon golem to service makes political enemies as easily as military allies. An intact weapon might save a town; in the wrong hands it could begin a war.
Related Golems, Weapons and Magic
Explore the golem family, Iron Golem, Stone Golem, Clockwork Golem, adamantine, Craft Construct and heat metal.
Rules reference: Pathfinder 1e Bestiary 3 — Cannon Golem (OGL); Legendary Games, Sea Monsters (5E) © 2021 (third-party OGL), with publisher and authors credited on the linked source page. The 2024 and 3.5e adaptations and all adventure material are original campaign additions, not official rules in those editions.
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