The Scottish landscape is thickly dotted with castles. Many stand ruined and isolated; others have been remodelled and extended into more spacious mansions. The transition from castle to country house was one of the most important changes in the Scottish landscape between 1500 and 1800. In 1500 many landed families were still living in castles which had originally been built in the thirteenth century. Tower houses were cheaper to build than curtain-wall castles yet were remarkably effective defensive structures combining maximum security with a modest outlay. In the Highlands the defensive role of the castle lasted longer than in the Lowlands. Many Highland castles played an important part in the Jacobite rebellions between 1689 and 1746. The first true classical country houses, using designs developed from those of Andrea Palladio in Italy, via the work of English architects like Inigo Jones, Vanbrugh and Wren, began to appear in Scotland in the later seventeenth century.