When we first met Leonardo da Vinci in number two, Ezio thought of him as a friend of his mom's. Then, when Ezio became an Assassin, he relied on Leonardo more and more, making them two close friends throughout number 2 and Brotherhood. The last you see of him is when he sells you supplies to climb better in Brotherhood. But in Revelations, you do not see him at all. Leonardo died on May 2, 1519, so historically, he was still alive during the time period of Revelations. But yet not a mention of his name, what happened? It's like they totally erased him from the game. I know Ezio was in a different place, but he didn't even speak of him. Ubisoft should have at least mentioned Leonardo in Revelations because he was so important in number 2 and Brotherhood.