There is evidence of human settlement on the northern coastline of Bahrain dating back to the Bronze Age. The Dilmun civilisation inhabited the area in 3000 BC, serving as a key regional trading hub between Mesopotamia, Magan and the Indus Valley civilisation. Approximately 100,000 Dilmun burial mounds were found across the north and central regions of the country, some originating 5,000 years ago. Despite the discovery of the mounds, there is no significant evidence to suggest heavy urbanisation took place during the Dilmun era. It is believed that the majority of the population lived in rural areas, numbering several thousand. Evidence of an ancient large rural population was confirmed by one of Alexander the Great's ship captains, during voyages in the Persian Gulf. A vast system of aqueducts in northern Bahrain helped facilitate ancient horticulture and agriculture.