Robben Island is roughly oval in shape, 3.3 kilometres (2 miles) long north–south, and 1.9 km (1+1⁄8 mi) wide, with an area of 5.08 km2 (1+31⁄32 sq mi). It is flat and only a few metres above sea level, as a result of an ancient erosion event. It was fortified and used as a prison from the late-seventeenth century until 1996, after the end of apartheid.