There are a few things you should get before you go to Rome: The Armor of Altair, The Sword of Altair (or whichever weapon you prefer), Notched Cinquedea, Metal Cestus, both knife belt upgrades (as many as possible), medium and large medicine pouches (buy as much medicine as possible), and full smoke bombs. The battle is divided into three stages. In the first stage you must assassinate him. Go down the ladder quietly. Do not jump down. Then begin blending in with everyone immediately. Go to the front, select your pistol, and lock on to Rodrigo. Hold [Action] until the thin beam appears and fire. In the second stage you must fight him. You sit back and wait for your four Dopplegangers to finish or at least weaken him, but you can also join in the fight which is much more exciting. He attacks just like a brute; just tackle him as you would a normal villain. In the third stage you must finish the job. After the cinematic, use Eagle Vision to find the switches to the vault. Follow the road down. Another cinematic starts, after which it is a fistfight from here on out. Just keep attacking him. The Metal Cestus will stay equipped and will kill him faster. Follow the onscreen prompt to finish the fight.