On Civ IV, the city I'm attacking has 40% defence. This is when I have no units selected. But when I select a unit it goes up to 100%. What in the world is happening? Any help would be appreciated. It's probably just some part of the game I didn't know about.

<Yeah, I missspellled the title. oops>

I think it's a bug and it will still take just as many turns with cats to bring down defences even though it says 40% but is counting down from 100%.

So would the city defence be 40% or 100%?

Unless 40 is culture defence and 100 is from walls and castle vs pregunpowder. I've just had the same happen to me.

City probably has 40% cultural defense and a castle, so when you don't have a unit selected it shows the 40% defense which works vs everything, but when you select a pre-gunpowder unit it shows the 100% defense from castle. If you look at stacks while selecting different units, you'll see the unit 'on top' switch to whatever would defend against the selected unit too.

If you select a non-gunpowder unit it will give you the odds for a wall and castle but gunpowder units don't regard the wall and castle and are only effected by the cultural bonus

There is a bug with bombardment of defenses. The event log would say 'you lowered them to 30%, yet the city defense icon would show something higher.
It uses whatever value is higher, either cultural or castles/walls not a combination of both. As the previous posts say it would provide the best defense possible against whatever unit is thrown against it at that time.

Thats strange.. I've had it the other way round.

A city said 40%, and I bombarded it down to 32%, and the event log said I bombarded it down to 80%.

32 is 80% of 40... so I guess its just reporting the wrong number.

I've had this issue during bombardments as well. I just keep bombarding until I can't anymore, and that is 0%.

I've had this issue during bombardments as well. I just keep bombarding until I can't anymore, and that is 0%.

good way to be sure 0 is 0!