<P> In the west, the Tanguts took control of the Ordos region, where they established the Western Xia dynasty . Although the Tanguts were not traditionally known for building walls, in 2011 archeologists uncovered 100 kilometres (62 mi) of walls at Ömnögovi Province in Mongolia in what had been Western Xia territory . Radiocarbon analysis showed that they were constructed from 1040 to 1160 . The walls were as tall as 2.75 metres (9 ft 0 in) at places when they were discovered, and may have been around 2 metres (6 ft 7 in) taller originally . They were built with mud and saxaul (a desert shrub) in one section, and dark basalt blocks in another, suggesting that the rocks may have been quarried from nearby extinct volcanoes and transported to the construction site . Archaeologists have not yet found traces of human activity around this stretch of wall, which suggests that the Western Xia wall in this location may have been incomplete and not ready for use . </P> <P> In the 13th century, the Mongol leader Genghis Khan, once a vassal of the Jurchens, rose up against the Jin dynasty . In the ensuing Mongol conquest of the Jin dynasty, the nomadic invaders avoided direct attacks on the Jin fortifications . Instead, when they could, the Mongols simply rode around the walls; an effective example of this tactic is in 1211, when they circumvented the substantial fortress in Zhangjiakou and inflicted a terrible defeat upon the Jin armies at the Battle of Yehuling . The Mongols also took advantage of lingering Liao resentment against the Jin; the Khitan defenders of the garrisons along the Jin walls, such as those in Gubeikou, often preferred to surrender to the Mongols rather than fight them . The only major engagement of note along the main Great Wall line was at the heavily defended Juyong Pass: instead of laying siege, the Mongol general Jebe lured the defenders out into an ambush and charged in through the opened gates . In 1215, Genghis Khan besieged, captured, and sacked the Jin capital of Yanjing (modern - day Beijing). The Jin dynasty eventually collapsed following the siege of Caizhou in 1234 . Western Xia had already fallen in 1227, and the Southern Song resisted the Mongols until 1279 . </P> <P> With that, the Yuan dynasty, established by Genghis Khan's grandson Khublai Khan, became the first foreign dynasty to rule all of China . Despite being the head of the Mongol Empire, Khublai Khan's rule over China was not free from the threat of the steppe nomads . The Yuan dynasty faced challenges from rival claimants to the title of Great Khan and from rebellious Mongols in the north . Khublai Khan dealt with such threats by using both military blockades and economic sanctions . Although he established garrisons along the steppe frontier from the Juyan Lake Basin in the far west to Yingchang in the east, Khublai Khan and the Yuan emperors after him did not add to the Great Wall (except for the ornate Cloud Platform at Juyong Pass). When the Venetian traveller Marco Polo wrote of his experiences in China during the reign of Khublai Khan, he did not mention a Great Wall . </P> <P> In 1368, the Hongwu Emperor (Zhu Yuanzhang, r . 1368--98) ousted the Mongol - led Yuan dynasty from China to inaugurate the Ming dynasty . The Mongols fled back to Mongolia, but even after numerous campaigns, the Mongol problem remained . </P>

When did the building of the great wall of china start and end