Assassin's Creed 2 Walkthrough

There are four areas of the city, all east of your current location, that require "clearing." Which is to say, you need to go to these four locations and kill the brute guards, the heavily-armored guys that show up in gold with your eagle vision. Each of these areas has standard guards nearby as well, but you don't need to kill them. Move to the nearest area and you'll find two of these brute guards standing on a bridge. Approach them subtly and you can assassinate both without a fuss.

The next area that needs clearing is a ship in the river that runs through the city. The ship is considered a restricted zone, so you can't just waltz onto it. But you can board the ship from the water, climbing onto the side of it to peek above and make sure no one on the deck is watching you. There are two more brutes patrolling the ship's deck and you can easily slip behind them for another double assassination.

The last two areas are pretty close by, and each is marked by multiple targets. To the south are two brute guards on opposite ends of a walkway by the river. You can chill in the water, cling to the ledge of the walkway, and wait for each guard to get near you for a quick assassination from the ledge. Beware that there are small restricted areas marked on the map, and if you swim through their edges the lesser guards on the walkway will spot you.

To the north, the group you have to kill is actually made of three archers on the rooftops. Getting to them stealthily isn't easy because of their formation, but since they're just archers there's no real reason to play it so safe. Just rush the clowns. When all three are dead, the mission is ended.