The exact location of the sunken city is disputed, but the most common opinion is that the city lies east of the Kyrgyz capital Bishkek. It is often assumed that the city was located near the Burana Tower, named after the neighboring town of Burana.
The city was founded by the Sogdians of Iranian descent and was first mentioned in written sources dating to around 942. Shortly afterwards, the Turkish Karakhanids conquered the city and made it the capital of their empire. After the empire was divided in the middle of the 11th century, Balasagun was only the capital of the Eastern Empire. The Karakhanid rulers were so weakened in 1134 that the Kara Kitai were able to easily take the city and make it their capital. The rule of the city changed again in 1211, when the son of the former leader of the Mongolian Naimans came to power. He was in conflict with Genghis Khan and his governance also lost the sympathy of the city's population. This meant that Genghis Khan's Mongols were able to easily take over the city around 1217. After that, the city began to decline, and no sources are known about its subsequent development (Wikipedia).