A form of architecture in which a hollow circular column of 50-150 feet high is capped by a short pointed roof of stone. There are many in Ireland (upwards of 100), also in Scotland, the Isle of Man, in Denmark, and as part of Windsor Castle in England. Round towers were a feature of Irish monasteries from the Viking period and into the Romanesque. There is usually a single entrance door, about 8-15 feet above the ground, usually five stories high, and each floor was lit by a separate window and had a wooden floor. Because the doors were placed high off the ground, it seems that the main function of the towers was as a refuge from Viking and Irish raiders, but they may also have been used as companiles.