I first want to preface this post with a huge SPOILER warning.
In Assassin’s Creed II, Ezio has the task of sneaking into the Vatican – probably the only game in history where we’ve have the honor of doing this. It’s one of the trickiest parts of the game and it will take more than one chance so don’t lose patience and don’t give up.
If you’re stuck at this point in the game, I’ve compiled a few pointers from forum members.
The first piece of advice comes from bango31. It’s probably the best solution on how to get in.
Blend with the first group of monks and wait for the guard to walk past. As soon as he has his back to you, get moving. Tail him and fall in to the next group of monks. Now the two guards that patrol that area are always on opposite sides of the dividing walls, so you have two options.
You can either assassinate the guard further up ahead (when he’s on the left side of the dividing wall) or you can tail him, go to the last half-wall thing, hop over and hit the lever really quickly.
I took him out before he rounded the corner towards the two guards on the other side, then darted to that last half wall, made the hop over, hit the lever, and booked it.
The next tip comes from diggity1974:
Blend with the monks and stealth assassinate the guards when they walk by. Proceed to guard 2, rinse and repeat. Walk up behind the last 2 and take both out with hidden blades. Walk you merry way around. Viola!
If you have any further questions, please post a comment.

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really easy way, all you gotta do is blend with the first set of monks, follow the guard around, and blend around there. then move to the next monks, get your smoke bomb out. run around the corner, throw it, then hit the switch and run through
You seem to be forgeting poison. Blend with the first moving group of guards and behind the first guard. Stealth assassinate him with poison and then take out the others while they gawk at him flailing.
Sorry I meant to write group of monks
This part was easy. I did it in one shot. My most embarrassing mission was the 40-someodd attempts at the “flying” machine. I swear, the game cheated on at least three of those tries.
if you watched the 2 guards they never walked around the wall at the same time. I thought how will I ever get a chance to get to the gate? THEN I realised they do a SPIN and WAVE … they do it at differant times but once they both do it they become insync with there walks around the walls giving you the chance to go double assassinate the guards while the walking guards are on the opposite side.. hit the lever and peace out lol.
Many ways to do it I guess.
i am right at the beginiog of the mission and i can’t get in/What do i have to do?