Aren't the spies uber-powered during the sieges?

[Handel]

It is easy to enter 3 epies 4-5 starts each in the targeted city/castle. Then you can attack and take the city in the same turn without any siege machines.

[Quillan]

I don't consider them overpowered. For starters, gaining skill increases on spies is easy. If the city contains even two reasonably skilled spies, you won't be dropping 5 spies into the settlement prior to assaulting, unless you're just doing that in the hopes that one will survive. For another, all the spy does is open the gate. It makes a huge difference if the target settlement is weakly garrisonned, but if the garrison is strong, the Charlie-Foxtrot that will be the mass rush through the gate will get the bulk of your army slaughtered on the spot. And, if your army really overpowers the defenders in numbers as well as strength, you'd win without the spies so it really doesn't make that much of a difference. The one place where it makes a difference is it allows you to make an immediate assault if you didn't drag slow moving artillery along in the army.

[Handel]

The point is exactly in making the aproach and the capture in one turn. This way the enemy has no time to bring reinforcements and the Pope has no time to intervene.

[Quillan]

I've made many without spies. Just drag along artillery.

[Darkmoor_Dragon]

I've made many without spies. Just drag along artillery.

Spies move further than artillery, artillery doesn't move as far as an army. His point is valid in that regard.

However, it is easy to maintain at least one spy per town/castle as the human player to help avoid such instances, really the AI should do the same. Upon checking though you will often find some places with 4-6 spies and other towns with none at all.

[Decker]

How does the spy open the gate? Do you have to do it manually or is it automatic?