Sieges are the most troublesome invasion that my colony faces. The mortars keep setting fires and destroying walls, sending colonists outside to repair, who then get injured by mortar fire. It requires a great deal of micromanaging to minimize the damages.

Attacking the siege is dangerous; without the aid of my defenses, all I have is colonists taking fire and frequently dying or losing limbs. Each siege can be very costly.

My question is, what triggers an event to be a siege rather than a standard attack? Is it a wealth threshold, is it the way you have built your colony, research level, or is it completely random?

From my own observations, they seem to only happen once I'm settled in, which suggests wealth - but I've also built up my defenses and walls at this point.

2 Answers 2


In Rimworld a siege is considered an "event". Events are random, meaning we have no idea what triggers them.

I, like you, have only experienced sieges once I am well into my colony. There is no real way to tell what/when triggers them unless you were to dig into the code and factor in things like difficulty and storyteller.


My recent colony grew in population pretty quick and I also noticed the sieges appeared earlier than I'm used to. So drawing a conclusion from this I'd say population is probably a factor. Think I had 6 pawns when first siege came.

I was a lucky owner of two sniper rifles (that cost my butcher two arms and my farmer both legs! argh!) and the two are great siege breakers sniping them down from afar. A melee backup is also good if a bandit engages them hand to hand.

  • Once you have your own mortars, counter-battery fire is another viable alternative. Incendiary rounds work well if the besiegers set up in a vegetated area, but less so if they show up while it's raining.
    – Landric
    Mar 10, 2015 at 9:46
  • I've never hit anything with them =P Just making my pawns hungry and sleepy when the pirates start their assault, hehe =)
    – Tapirboy
    Mar 10, 2015 at 12:35
  • 1
    I belive mortar accuracy is also influenced by shooting skill. In my last colony, I had bought a shooting neurotrainer, and managed to take out or cripple some of the sieges with just mortar fire. Apr 17, 2015 at 9:00
  • @EagleV_Attnam That makes so much sense. I've always put the useless (for battle) at the mortars to keep my assault team fed up and rested when the heat begins. Guess I'll have to change that..
    – Tapirboy
    Apr 17, 2015 at 10:06

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