Kara Khoto city was founded in 1032 and became a thriving center of Tangut Empire trade in the 11th century. There are remains of 30-foot (9.1 m)-high ramparts and 12-foot (3.7 m)-thick outer walls. The outer walls ran for some 421 m (1,381 ft) east-west by 374 m (1,227 ft) north-south. The walled fortress was first taken by Genghis Khan in 1226, butcontrary to a widely circulated misunderstandingthe city continued to flourish under Mongol overlordship. During Kublai Khan's time, the city was expanded, reaching a size three times bigger than during the Tangut Empire. Togoontemur Khan concentrated his preparation for reconquest of China at Khara-Khoto. The city was located on the crossroads connecting Karakorum, Xanadu and Kumul. In The Travels of Marco Polo, Marco Polo describes a visit to a city called Etzina or Edzina, which has been identified with Khara-Khoto.