Ireland has a wealth of structures, surviving in various states of preservation, from the Neolithic period, such as ''Brú na Bóinne'', Poulnabrone dolmen, Castlestrange stone, Turoe stone, and Drombeg stone circle. As the Romans never conquered Ireland, architecture of Greco-Roman origin is extremely rare. The country instead had an extended period of Iron Age architecture. The Irish round tower originated during the Early Medieval period.