Shangdu was built between 1252 and 1256 by Liu Bingzhong, a former Buddhist monk who served as a trusted advisor to Kublai Khan. Liu designed the city with what historians call a 'profoundly Chinese scheme' -- Confucian principles of city planning adapted to the open steppe. The result was a triple-walled city: an outer city, an inner city, and a central imperial palace whose enclosure measured roughly 550 meters per side, about 40 percent the size of what would later become Beijing's Forbidden City. Originally named Kaiping, the city was renamed Shangdu -- meaning 'Upper Capital' -- in 1264, when Kublai Khan designated it his summer capital. Located 350 kilometers north of Beijing in the grasslands of present-day Zhenglan Banner, it served as a seasonal retreat where the Khan could escape the heat of the lowlands while maintaining court functions, receiving foreign envoys, and hunting in the surrounding parklands.

Marco Polo visited Shangdu around 1275 and left descriptions that would echo through centuries of Western imagination. He described a marble palace with gilt rooms, an expansive park enclosed by walls, and a portable palace made of cane and lacquered bamboo, adorned with dragons and engineered to be dismantled and transported wherever the Khan wished to travel. Archaeological findings have confirmed key elements of Polo's account: marble architectural elements, gilded decorations, and elaborate wood and lacquer work have been recovered from the site. At its height, Shangdu had a population exceeding 100,000, with gardens, hunting grounds, temples, and administrative quarters supporting a cosmopolitan court that embodied the synthesis of Mongol governance and Chinese administration.

In 1369, during the collapse of the Yuan dynasty, Ming forces sacked Shangdu. The court fled north. The city was abandoned and never recovered. For centuries, the ruins lay largely undisturbed on the grasslands. In 1872, British diplomat Steven Bushell visited the site and recorded surviving remnants -- temple foundations, marble blocks, decorative tiles. But by the late 20th century, much of this material had been scavenged by residents of nearby Dolon Nor for building use. What the conquerors did not destroy, the pragmatic needs of local construction slowly dismantled. Since 2002, the Chinese government has undertaken preservation and study of the ruins, and in 2012, Shangdu was designated a UNESCO World Heritage Site for its cultural and historical significance.

Coleridge's poem was inspired not by Polo directly but by the account of English clergyman Samuel Purchas, who in 1614 described 'Xandu' based on earlier sources. Coleridge, reading Purchas while under the influence of opium, fell asleep and dreamed an entire poem about the pleasure palace. He woke and began writing furiously -- then was interrupted by a visitor from the nearby town of Porlock and found, when the visitor left, that the rest of the poem had vanished from his memory. What survived -- 54 lines of vivid, musical verse -- became one of the most celebrated fragments in English poetry. The name Xanadu entered the English language as shorthand for any place of extravagant luxury. It named the mansion in Citizen Kane, a Rush song, a 1980 musical film, and a region on Saturn's moon Titan. Kublai Khan's summer capital may have lasted barely a century as a living city, but its afterlife in the Western imagination has now endured for more than seven hundred years.