Early Medieval architecture's secular buildings were simple constructions mainly using timber with thatch for roofing. Ecclesiastical architecture ranged from a synthesis of Hiberno–Saxon monasticism, to Early Christian basilica and architecture characterised by pilaster-strips, blank arcading, baluster shafts and triangular headed openings. After the Norman conquest in 1066 various Castles in England were created so law lords could uphold their authority and in the north to protect from invasion. Some of the best-known medieval castles are the Tower of London, Warwick Castle, Durham Castle and Windsor Castle.