In May 1275, Kublai Khan welcomed the Polo brothers, and Niccolò Polo's son Marco into his court, not knowing that the famed explorers were in fact Assassins. The Polos' alliance with the Khan and Marco's seventeen years of service gave the latter the opportunity to break into Kublai's vault in Chengdu and steal back Altaïr Ibn-La'Ahad's Codex, which had been taken by the Mongols from the two elder Polos to whom Altaïr had entrusted it.