Round Towers, ancient towers, found chiefly in Ireland, of a tall, round, more or less tapering structure, divided into storeys, and with a conical top, erected in the neighbourhood of some church or monastery, and presumably of Christian origin, and probably used as strongholds in times of danger; of these there are 118 in Ireland, and three in Scotland—at Abernethy, Brechin, and Eglishay (Orkney).
Definition taken from The Nuttall Encyclopædia, edited by the Reverend James Wood (1907)
Round Table, The * Roundheads