In the Kathmandu valley, the Kiratas were pushed eastward by the Lichchhavis, and the Lichchhavi dynasty came into power  400 AD. The Lichchhavis built monuments and left a series of inscriptions; Nepal's history of the period is pieced together almost entirely from them. In 641, Songtsen Gampo of the Tibetan Empire sends Narendradeva back to Licchavi with an army and subjugates Nepal. Parts of Nepal and Licchavi was later under the direct influences of the Tibetan empire. The Licchavi dynasty went into decline in the late 8th century and was followed by a Thakuri rule. Thakuri kings ruled over the country up to the middle of the 11th century AD; not much is known of this period that is often called the dark period.