Ac 2 v 23 - Peacekeeper
0Unlocked After: Sequence 5 - Memory 1: Four to the Floor
Kill 10 Brutes within one minute -- it's easier than it sounds. Make your way to the bridge that the Brutes are stationed on and equip your Hidden Blades by pressing up on the D-pad. The first set of Brutes should be facing the north, and the second set further up should be facing south. If they are walking around, wait until both groups have their backs turned to each other. Walk past the first set of Brutes and use your Hidden Blades to score double kills on the second group of Brutes while their backs are turned. With any luck, you should be able to wipe them all out without being detected.
Take to killing the second group once the first has been dealt with. Attempt to do the same by approaching the group from behind and going for double kills. If one or two Brutes are on to you, you should still have enough time to dispatch of them some other way. You can easily kill a single Brute if you happen to have the Disarm skill: unequip your weapon by pressing down on the D-pad, then hold RT/R2 and tap X/Square just as the Brute attacks -- the same as you would to perform a Counter Kill. Then you can use his own weapon to quickly end him. - https://www.supercheats.com/guides/assassins-creed-ii/