Originally Posted by Tyger7
Prince of Thieves 10
Loot a convoy without killing any of its guards.
A convoy is a horse-drawn carriage that is guarded by some soldiers and a drummer. They can only be found in the Frontier area. There are fixed spawn points for them, but they can also appear randomly at any daytime and weather condition. One of these convoys has a 50% spawn chance in front of the Templar Fort that is located in the south-western corner of the map. There is a harbor nearby that can be used as a fast travel station. If the convoy doesn't spawn you can travel to another map and return later. To actually loot the convoy without killing anyone you just have to use your fists instead of lethal weapons. This will knock your enemies out and not kill them. You can also use smoke bombs to stun the soldiers and finish them more quickly. Once all guards are defeated you have to interact with the back of the carriage for some nice loot. This technique can also be used to farm money quickly!
Assassin's Creed 3 - Prince of Thieves Trophy / Achievement Guide - YouTube
Should point out that the video here does not work. I finished a convoy with just using my fists, and the achievement didn't unlock for me. It wasn't that convoy, though, but another one on the map. I doubt which convoy makes any difference.