Genghis Khan and his Mongol horsemen thundered across Asia, creating the largest empire the world has ever known. The Mongols were ferocious warriors, but they imposed peace on the lands they conquered. It became possible to travel and trade safely from Europe to the Orient. Grandson of Genghis, Kublai Khan conquered and united the whole of China but was seduced by luxury in his palace at Xanadu. The Mongol advance west was finally halted by the Mamelukes, a Muslim dynasty of former slaves who made Cairo into one of the world's greatest cities. Goods and ideas from the Orient traveled via Venice up into northern Europe.