Historians have interpreted the widespread presence of castles across Europe in the 11th and 12th centuries as evidence that warfare was common, and usually between local lords. Castles were introduced into England shortly before the Norman Conquest in 1066. Before the 12th century castles were as uncommon in Denmark as they had been in England before the Norman Conquest. The introduction of castles to Denmark was a reaction to attacks from Wendish pirates, and they were usually intended as coastal defences. The motte and bailey remained the dominant form of castle in England, Wales, and Ireland well into the 12th century. At the same time, castle architecture in mainland Europe became more sophisticated.