When do sieges start?

I have been playing for about two in-game years now and still no sieges. I am kind of relieved, but also worried one might happen soon.

I read on the forums that sieges start happening when there's a mayor, but I can't find any information on the wiki. Can anyone shed some light on this?

Goblin sieges happen when you have goblins on your map and you have met certain conditions.

These conditions include

• Number of dwarves
• Amount of things traded

How you've dealt with other goblin invaders earlier also effects the timing of the siege. If goblin ambushes were allowed to get a lot of kills the siege may come earlier.

If you haven't seen goblin snatchers or goblin ambushes yet, you probably don't have goblins around to siege. If you want one you should anger the elves or humans.