Siege Engines in DnD 5e

Last Updated on October 24, 2023

At some point, your character needs to take their own reputation seriously and consider investing in a weapon of mass destruction. This post is your guide on how to do just that.

How Do Siege Engines Work in DnD 5e?

Siege Engines are large weapons that often take multiple creatures and multiple rounds to operate. The resulting attack from siege engines deals massive damage on par with many higher-level spells. These weapons are typically used to damage structures and fortifications.

Why Would You Need a Siege Engine?

The real question is, why wouldn’t you want one? When your character is at a high-enough level that they could trade in a magic item for enough gold to buy a ballista and a team of engineers to operate it, you have truly achieved legend status and should revel in it.

Sure, there are the logistics of traveling with such a crew and their tackle, but the look on Strahd’s face when you launch a giant crossbow bolt enchanted to deal radiant damage at his front door will absolutely be worth it. Or even better, a trebuchet that launches clay pots that are filled with holy water! Can you even call yourself an artificer if you can’t engineer a collapsible mangonel?

Honestly, it’s time you up your game a little bit. So what if you can cast Earthquake? Who cares if you can single-handedly slay a dragon? Until you can manage to lead a platoon of moderately trained soldiers and point their heavy payload at the castle, there is no guarantee the king will pay you for your monster hunting.

Damaging Structures

The Dungeon Master’s Guide offers a fair bit of guidance for dealing damage to objects.

It all boils down to four things that you need to consider: Armor Class, Hit Points, Damage Types, and Damage Resistance (threshold).

1. Armor Class

An object’s Armor Class is a measure of how difficult it is to deal damage to the object when striking it (because the object has no chance of dodging out of the way).

It is assumed you will hit the thing you are aiming at, especially if it is something as big as, say, a castle wall or a portcullis. Therefore, the Armor Class of a structure does not represent whether you hit — it represents whether you will hit it hard enough to do damage.

The chart below shows the suggested armor class of your structures, considering what they are made of.

Object Armor Class

2. Hit Points

An object’s hit points measure how much damage it can take before losing its structural integrity. Resilient objects have more hit points than fragile ones. Large objects also tend to have more hit points than small ones.

The DMG then goes on to give a chart offering Hit Point values for various objects from small glass bottles to large wooden carts. Structures are much larger than these, and fortified structures will be even more difficult to damage.

When trying to consider how many Hit Points a structure has, I suggest giving each 10-foot by 10-foot section of the structure a number of Hit Points equal to its Armor Class times 3.

3. Damage Types

Structures are immune to poison and psychic damage. You might decide that some damage types are more effective against a particular object or substance than others.

A wooden structure might take normal damage from slashing but have resistance to piercing and vulnerability to lightning or fire.

A stone structure might take normal damage from bludgeoning but have resistance to piercing and slashing and vulnerability to acid.

4. Damage Threshold

In some cases, it may be appropriate to consider that the structural integrity of the entire building might reinforce the small part you are trying to damage. Therefore, you may consider that the building doesn’t take any damage at all unless you can deal a certain amount of damage to it first.

This means, for example, that a wooden wall could have 45 Hit Points, but it takes lots of wear and tear over the years and still stands tough. You may need to deal half of its total hit points in order for any damage to make it through that natural toughness.

This goes beyond a structure’s armor class and should only be considered if the structure was designed to take damage and serve as a defensive position.

A castle wall might have this feature, but not a merchant stall.

The List of Siege Engines

What Is a Siege Monster?

Siege Monsters are those monsters that seem to greatly enjoy dealing damage to structures made by humanoids who take great pride in their cities.

Many of them are quite large and can be seen happily kicking down skyscrapers or crushing vehicles when they aren’t sleeping between the apocalypses they cause.

They all bear the siege monster trait, which allows them to deal double damage against objects and structures.

In general, these monsters have Kaiju status.

This is not meant to be a complete list, but it should be fairly thorough. Each one of these is worth taking a look at either on your DnD Beyond account or here at BCRPG.

Final Thoughts

Don’t get stuck thinking in the same small-minded mode you were forced into at 1^st level. It’s more than just you and your sword.

Expand your business by getting the tools to destroy someone else’s!