Agriculture was being practised in southern Britain by 4000 BCE, and with it a neolithic culture. Some deforestation took place at that time, although during the Bronze Age, beginning in 2200 BCE, this became more widespread and systematic. Hampshire has few monuments to show from these early periods, although nearby Stonehenge was built in several phases at some time between 3100 and 2200 BCE. In the very late Bronze Age, fortified hilltop settlements known as hillforts began to appear in large numbers in many parts of Britain including Hampshire, and these became more and more important in the early and middle Iron Age; many of these are still visible in the landscape today and can be visited, notably Danebury Rings, the subject of a major study by archaeologist Barry Cunliffe. By this period, the people of Britain predominantly spoke a Celtic language, and their culture shared much in common with the Celts described by classical writers.