I passed the "build X colosseums" quest, by conquering 3 of my neighbours. Number of colosseums actually built: 0. Unfortunately, this has the downside of number of colosseums affected by this quest: 0
EDIT: Actually, nevermind, they are affected. I thought cities not actually founded by you were unaffected by quests such as these. I was almost certain of it, having , I could have sworn, seen things like newly conquered cities being unaffected by bonuses to harbours from harbour affecting quests (think there are 2 if I'm not mistaken), etc. Weird. Anyway, works out for me.
EDIT: Actually, nevermind, they are affected. I thought cities not actually founded by you were unaffected by quests such as these. I was almost certain of it, having , I could have sworn, seen things like newly conquered cities being unaffected by bonuses to harbours from harbour affecting quests (think there are 2 if I'm not mistaken), etc. Weird. Anyway, works out for me.