That preacher on the duomo drove me nuts. But it really made me think and was very satisfying in the end. Here's how I did it in case people are stuck on this bastard: Climb the corner wall, hang kill the first guard. Climb around the corner, then up, then jump kill the next guard. Go left and jump kill the guard below. There will be one guard on the same floor and one on the roof to the right. Climb the roof rail until the roof guard is close enough to hang kill. Go to the other side of the roof and throw knives to kill the guard by the haystack. Get back on the edge of the roof and kill the middle guard. Climb up and wait for the archer on the right to go all the way around. This should give you just enough time to kill the guard on the right. After that kill the preacher once the other archer walks back around.