The history of Himachal Pradesh dates back to the time when the Indus valley civilisation flourished between 2250 and 1750 BCE. Tribes such as the Koilis, Halis, Dagis, Dhaugris, Dasa, Khasas, Kinnars and Kirats inhabited the region from pre-histotic era. During the Vedic period, several small republics known as "Janapada" existed which were later conquered by the Gupta Empire. After a brief period of supremacy by king Harshavardhana, the region was once again divided into several local powers headed by chieftains, including some Rajput prinicipalities. These kingdoms that enjoyed a large degree of independence were devastated by Muslim invaders a number of times. Mahmud Ghaznavi conquered Kangra at the beginning of the 10th century. Timur and Sikander Lodi also marched through the lower hills of the state and captured a number of forts and fought many battles. Several hill states acknowledged Mughal suzerainty and paid regular tribute to the Mughals.