Tower houses began to appear in the Middle Ages, especially in mountainous or limited access areas, in order to command and defend strategic points with reduced forces. At the same time, they were also used as an aristocrat's residence, around which a castle town was often constructed.
- Sidney Toy (1985) Castles: Their Construction and History, Courier Dover Publications, ISBN 0-486-24898-4 (reissue of Castles: a short history of fortification from 1600 B.C. to A.D. 1600; London: Heinemann, 1939)
- A. Mackechnie, "'For friendship and conversation': Martial Scotland's Domestic Castles" Architectural Heritage XXVI (2015), pp. 14, 21.
- Grube-Mitchell 1978, p. 204: "a distinctive form of defensive tower-dwelling, the kula, developed among both the Christian and the Muslim communities during the insecure period of the decline of the Ottoman authority in the 17th century ..."
- Greville Pounds 1994, p. 335: "In southeastern Europe, where the extended family was exemplified as nowhere else in the western world, the home itself was often protected, giving rise to the kula or tower- house."
- Tower house structure at Mesa Verde
- Johnson Westropp, Thomas (1899). "Notes on the Lesser Castles or 'Peel Towers' of the County Clare". Proceedings of the Royal Irish Academy. 20: 348–365.
- Greville Pounds, Norman John (27 May 1994). The Culture of the English People: Iron Age to the Industrial Revolution. Cambridge University Press. Retrieved 10 May 2012.
- Ernst J. Grube, George Michell (1978). Architecture of the Islamic world: its history and social meaning, with a complete survey of key monuments. Morrow. Retrieved 10 May 2012.