The Portlandian sequence comprises a variety of lithologies. some of which have traditionally been used as building stones since Roman times. The geology and engineering properties of the Portlandian building stones are presented and compared with the published acceptance limits for use of rock armour in marine works. A review of the historical use and performance of Portland rock in nineteenth century breakwaters in Dorset indicates that the rock performs adequately. Details are given of the selection and use of rock armour from the Isle of Portland in recent coast protection and sea defence works and details of the rock performance are presented.