The Indus Valley Civilisation is also named the Harappan Civilisation after Harappa, the first of its sites to be excavated in the 1920s (mainly 1921), in what was then the Punjab province of British India. The discovery of Harappa, and soon afterwards Mohenjo-daro, was the culmination of work beginning in 1861 with the founding of the Archaeological Survey of India in the British Raj. Excavation of Harappan sites has been ongoing since 1920, with important breakthroughs occurring as recently as 1999. This Harappan civilisation is sometimes called the Mature Harappan culture to distinguish it from the cultures immediately preceding and following it. Of these, the earlier is often called the Early Harappan culture, while the later one may be referred to as the Late Harappan, both of which existed in the same area as the Mature Harappan Civilisation. The early Harappan cultures were preceded by local Neolithic agricultural villages, from which the river plains were populated.