A tower house is a particular type of stone structure, built for defensive purposes as well as habitation. Tower houses began to appear in the Middle Ages, especially in mountainous or limited access areas, 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. After their initial appearance in Ireland, Scotland, the Frisian lands, Basque Country and England during the High Middle Ages, tower houses were also built in other parts of western Europe, especially in parts of France and Italy. In Italian medieval communes, urban palazzi with a very tall tower were increasingly built by the local highly competitive patrician families as power centres during times of internal strife. Most north Italian cities had a number of these by the end of the Middles Ages, but few now remain, notably two towers in Bologna, twenty towers in Pavia and fourteen secular towers in the small city of San Gimignano in Tuscany now the best group to survive. Scotland has many fine examples of medieval tower houses, including Drum Castle, Craigievar Castle and Castle Fraser, and in the unstable Scottish Marches along the border between England and Scotland the peel tower was the typical residence of the wealthy, with others being built by the government. In 17th century Scotland these castles became the pleasure retreats of the upper classes. While able to adopt a military nature, they were furnished for comfort and social interaction. Tower houses are commonly found in northern Spain, especially in the Southern Basque Country, some of them dating to the 8th century. They were mainly used as noble residences and were able to provide shelter against enemies, starting with the Arabs and later Castile and Aragon. Due to complex legal charters, few had boroughs attached to them, thus they are usually found standing alone in some strategic spot like a crossroad, rather than on a height.