I just picked up the game, so this might just be me being blind, but I picked up the tech Organized Warfare, and am now besieging a city, but have no option to build a siege engine? Is the option not in the battle screen?

The option should pop in when you start the siege.  The UI at the top should say something like "Prepare your assault" and building siege weapons (which happens slowly automatically as long as you don't attack and the enemy doesn't sortie) would be below that.

What might have happened, is, that the AI attacked you when you moved next to it before you clicked on them. In this case you would not be conducting a siege, but defend your flag (as besieger you don't have a flag) and you would not have access to siege equipment. This happens fairly often, and it is thus not advisable to bring an army that requires siege (e.g. all cavalry which cannot move through walls).

Often the ai sorti like a few moments after you start siege one of their cities, which will start a battle with you being defender, which is why you can't build siege weapons. Yes you can't build siege weapons during a battle and if you win against their sorti you should occupy their city anyway.

Ah, that's definitely what happened. Kind of annoying that the AI gets to just prevent me from building siege engines entirely like that :/

Dman1791 wrote:

Ah, that's definitely what happened. Kind of annoying that the AI gets to just prevent me from building siege engines entirely like that :/

Yes it can be very annoying, especially if you use alot of cavalry which can't enter fortifications.

Does anyone know what the behavior of the defenders depends on? Why they try to attack and deny us the use of siege weapons?

Not sure, but I've read that comparative strength plays a role. If they are outmatched in strength, they might wait for occasionnal reinforcements. I believe that if both attacker and defender stength are close to equal, AI will still attempt a sortie because waiting will only make the attacker stronger and the defender weaker.

I also believe their decision depends on whether you have archers/ranged units and they don't, I had early game sieges that were met with immediate sortie the moment I reinforced with archers and seen AI sortie a lot less if they got to industrial militia.

like he said, if you win against their sorti you get the city- it's actually (probably) easier that way because if you are being attacked you have to defend your flag and the AI will 99% of the time go straight for your flag. this way you have like 80% better chance of luring them out and hiting them where they are unfortified. Also if they fail to get the flag in 3 turns or so (not 3 rounds, 3 turns- there is 3 rounds in a turn) they insta-lose and must run away. If they get the flag you have 1 turn to get it back which probably isn't too hard as if you lost it that probably means it's in a bad position like in a donut hole and/ or on a river :/ the cpu likes to put the flag on a river. a pro move is to just leave the flag open as bait if you have the firepower to kill a guy in 1 turn. Also if the flag is in a poor position, put yourself in front of it not on it- unf you won't know where the flag is until your first turn.

So anyway it's abrupt an annoying that this game features simultaneous turns rather than sequential so basically any time you roll up to a cpu army he says 'there you are!' and INSTANTLY attacks you. it's annoying cuz he gets the first attack (or he fortifies giving more defense until he moves) BUT it makes the game what it is IMO. It's one of the biggest difs between Humankind and Civ.