Karakorum (Qaraqorum, Qara Qorum, Kara Korum, Khara Khorum, Kharkhorin), located in the Orkhon Valley of Mongolia, served as the capital of the Mongol Empire from 1235 to 1260, or the period of the United Mongol Empire. It must be considered an “implanted” city; that is, a city built and populated with an immediate population rather than one that grew and evolved over time. Although Chinggis Khan (1162–1227) used the Orkhon Valley as a campaign headquarters in the later years of his career, his capital, Avarga, was situated in the Onan-Kerülen basin, which was also his homeland. Not until the reign of his son, Ögödei Qa’an (r. 1229–1241), the second ruler of the Mongol Empire, did the true city of Karakorum appear. While the court remained mobile and moved periodically through the Orkhon Valley, the city of Karakorum served as a constant destination for merchants, missionaries, diplomats, and others who sought to interact with the Mongol court. With a population of perhaps ten thousand people within the walled area, Karakorum could not compare with the metropolises of China nor Baghdad. It served its purpose and in some ways was perhaps the most cosmopolitan city of the 13th century. With the ascension of Qubilai Qa’an to the Mongol throne, Karakorum’s significance dwindled as Qubilai had constructed a new city called Daidu (Ch. Dadu) to serve as his capital in northern China. Having discovered the vulnerabilities of Karakorum during his rise to power, Qubilai determined to ensure the security of his reign by moving the capital to his domain in North China. The move relegated Karakorum to a provincial town. It remained so, though Karakorum experienced a brief revival as a capital after 1368 with the Northern Yuan Empire. In 1380, Ming armies sacked the city. The destruction was enough to end Karakorum’s existence as a city. Construction of the Erdene Zuu Buddhist monastery in 1585 revived the area’s importance. Using materials from the ruins of Karakorum, the monastery was built on the site of Ögödei Qa’an’s palace. The modern city of Kharkorin is adjacent to the monastery and site of medieval Karakorum and houses a museum dedicated to the historical city, while archaeological work continues on the site.