Rising in stone above the small peasant dwellings of turf and timber, the castle was a centre of administrative and judicial control, as well as a secure place in times of conflict. Castle Sween on Loch Sween is the earliest stone castle in Scotland, built in the 11th century with a Norman-style round-arched doorway leading into the centre of the quadrangular building, once roofed with timber. With its origins in the 12th century, Edinburgh Castle stands out as the archetypal royal Scottish castle. Built on an extinct volcano, it commanded a strong strategic position and served throughout much of its history as a resonant symbol of power and protection. The epitome of the romantic Highland castle, on the other hand, is the beautifully picturesque Eilean Donan on Loch Duich. Originally a small 13th-century castle of enclosure, it was used to garrison Spanish troops as part of the Jacobite Rising, and was destroyed by English warships in 1719. The present building is predominantly a reconstruction, initiated at the beginning of the 20th century, an immaculate three-storey keep perched on a rocky outcrop with a dramatic arched bridge.

Developments in warfare and architecture marched hand in hand, and 13th-century castles employed a number of defensive techniques: the use of catapults and assault towers, the strengthening of outer walls, and construction of round towers to allow for a better view of the base. The tall, thick walls of Dunstaffnage are topped with a crenellated wall walk and contain few windows but many well-placed firing slits; an outer defence like the moat at Rothesay, which was established around 1204, was also common. Natural defences such as rocky outcrops were particularly impenetrable; Dirleton Castle uses one to great advantage, its weaker side protected by three towers forcing outwards in an aggressive manner, and Stirling Castle is similarly well defended. Situated on a grassy hilltop, the reinforced tower at Bothwell Castle near Blantyre provided an effective last refuge in an attack.