Dolos

A dolos (plural: dolosse) is a reinforced concrete block in a complex geometric shape weighing up to 80 tonnes (88 short tons), used in great numbers as a form of coastal management to build revetments for protection against the erosive force of waves from a body of water. The dolos was invented in 1963 by South African harbour draughtsman Aubrey Kruger, and was first deployed in 1964 on the breakwater of East London, a South African port city. (Wikipedia)