What would be the proper mechanics and stats for playing a siege?

Question

This question is from @NewbieDM; asked today on Twitter:

Would it make sense, if creating a 4e siege, to make a monster stat block for the horde, with different attacks, arrows, catapults, etc, and then a companion char stat for defending force, to fight alongside pc's individual skirmishes? How does that sound?

The question, I'd hazard a guess, refers to this article on his site.

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_{This is due to Jeff's advice, and I have notified @NewbieDM of this posting. He was cool with it. I did this in part to attract more people to this site, and also because I found the question interesting.}

Answer 1

I'd say the best ways to represent a siege (I guess you mean something like the Battle at Helm's Deep) are:

• either one or more Skill Challenge(s)
• or gathering of some sort of Victory Points

Skill Challenges

With "Skill Challenge" I don't mean "replace the whole battle with a few skill checks" but rather use a skill challenge as a framework to connect single encounters into a single, massive, confusing, awesome Siege of Doom(tm).

When and how soon did the city learn of the threat and what precautions could be taken before the siege arrived? Can the PCs convince the city's ruler/council to spare some troops (perhaps even clerics or wizards that would be required elsewhere) for a plan the PCs came up with? Do the PCs manage to notice a trap or distraction and find the real attack or attempt to finally break the city?

All these can be answered with appropriate skill challenges, where the outcome of each single challenge determines the next step (and possibly combat encounter) the siege puts in front of the players.

Victory Points

The basic idea is that the outcome of the siege depends on the PCs' actions. The more beneficial actions the players succeed at, the more victory points they gather. The higher their final score when the siege's climax comes around the better the overall outcome (and chances of survival) of the besieged city and its inhabitants.

The DM can award victory points not only based on the result of combat encounters (e.g., whether or not the PCs managed to destroy or sabotage the enemy's siege towers, etc) but also for roleplaying or strategic decisions (Where did the PCs put the city's troops? How did they distribute any magical healing? What are the members of the mage guild supposed to do during the siege? etc.).

Something like this has been used in the official Scales of War adventure path. The first instance such a mechanic is used is in Part 6, The Temple Between:

• If the PCs gather 6 or less victory points, Overlook (a big dwarven city) is burnt to the ground and basically eradicated.
• If the PCs gather more than 6 but less than 15 points, the city is heavily damaged but survives the onslaught.
• If the PCs gather more than 15 points the city survives the siege largely unscathed and with most of its inhabitants and important NPCs alive.

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If you want to go with the "stats block" idea, I would not put the whole horde into a single stat block but rather sort the different enemy units into blocks. So you don't have a single elite/solo "monster", but several minion/normal/elite units composed of dozens or hundreds of orcs/zombies/whatever.

This not only solves some of the weird interaction with conditions @AceCalhoon mentioned, but also gives the PCs more possible targets. Do they take out the siege towers to protect the walls? Or do they take out the minion archer squads shooting volley after volley at the defenders? Or do they try to attack the elite siege commander squad that controls the horde?

Answer 2

Yes, this could make sense. The main concern you'll need to watch out for is scale (and the larger the forces involved, the more of an issue it becomes).

You need to be careful of the two extremes. If the "horde" stats are too high (too many hit points, defenses too high, etc.) you'll end up making the player characters largely irrelevant compared to the defending force. If the horde stats are too low, then it will start to feel like the player characters are wiping out an entire army single handedly (which may very well be what you're going for :) ).

You will also want to watch out for interactions with the various status conditions. Knocking a horde prone won't really feel right, and dazing them might be a little weird. So would having the entire defending force be "dying" and waiting for some healing. You might simply make them immune to most conditions, and work out some custom rules for what happens when the horde is reduced to zero hit points.

Were I running an adventure using a system like this, I would probably break each attacking force down into several individual "units," each representing some number of attackers or defenders. I think this would help give the battle a bit more flow.

I would also limit this to smaller battles, rather than truly epic clashes, escalating the size as the players progressed to higher tiers.

Answer 3

There are many different types of sieges, representing many different tech levels.

My favorite siege terms are "lines of circumvallation" and "lines of countervallation" wherin the enemy really wants to build a walled torus around the enemy citadel. They want walls on the inside to stop sallies from the defenders. And walls on the outside to stop attacks by wandering armies. (Kind of like wandering monsters, but bigger.)

An actual siege is a not hugely interesting war of attrition, as the defender really doesn't want to engage against a fortified attacker (otherwise it wouldn't be a siege) and the attacker doesn't have the resources for a "knock on the castle gates."

The best assumption is that attacking force and defending force have rough manpower counts that cancel each other out. Both forces also have a rate of attrition and rate of resupply. The players are best engaged trying to fiddle those rates, rather than attacking either force directly. Charging into prepared defenses is a non-epic way of dying quite horribly.

As a simple rule, players may draw upon the defending manpower count for their activities to get minions to help them. (Minions may have encounter powers like "call catapult" or may even represent artillery tasked to help the players.) Catapults are really worthless in any kind of PC level skirmish, as their Circular Error Probable in sighting in is.. depressingly low. They're fantastic at hitting prepared spots though, and can certainly feature as part of a prepared encounter by or against the PCs. Deaths, of course, directly impact the manpower count.

Of course, the opposition also can draw down their reserves. In a day-to-day sense, extra people can be out foraging and scouting. In an encounter sense, they represent extra minions on top of whatever the encounter calls for, depending on how confident the enemy commander is. A concentration of force isn't possible because it's assumed that the PCs allies are drawing attention away from the PCs.

Thus, to break a siege as defenders, the PCs will have to infiltrate the enemy camp and increase their rate of attrition past the defenders' rate of attrition. (Assassinating leadership seldom works very well, as leadership generally has stupid-good guards and is quite replaceable in a siege.)

Given that both defenders and attackers are playing the attrition game, tactics look much the same for both sides and the players can easily feature as the deciding factor in a siege without needing to introduce a MacGuffin. By having soldiers be minions and a squad of soldiers be a proper (large or huge) ally or opponent, it's possible to simulate manpower excesses.