Lucrezia is forced into a political marriage with Claudia by Cesare, who wants to unify the Borgia and Auditore families in an attempt to end the Templar/Assassin feud. Because he loves peace and loves LOVE. And then they can all live together happily like the Brady Bunch, which will successfully bring him closer to his goal of getting into Ezio's MANPANTSS (because he knows exactly how he would welcome a man like that).

Also, Leonardo is the live-in inventor who bones everyone.