Bhutan's early history is steeped in mythology and remains obscure. Some of the structures provide evidence that the region has been settled as early as 2000 BC. According to a legend it was ruled by a Cooch-Behar king, Sangaldip, around the 7th century BC, but not much is known prior to the introduction of Tibetan Buddhism in the 9th century, when turmoil in Tibet forced many monks to flee to Bhutan. In the 12th century, the Drukpa Kagyupa school was established and remains the dominant form of Buddhism in Bhutan today. The country's political history is intimately tied to its religious history and relations among the various monastic schools and monasteries.