Scotland during the Roman Empire for ritualistic purposes, in the west and north. Their geographical locations are highly restricted, which suggests that they may have been contained within a political or cultural frontier of some kind and the co-incidence of their arrival and departure being associated with the period of Roman influence in Scotland is a matter of ongoing debate. It is not known whether the culture that constructed them was "Pictish" as such although they would certainly have been known to the Picts. As Rome's power waned, the Picts were emboldened. War bands raided south of Hadrian's Wall in earnest in 342, 360, and
Architecture of Scotland Trimontium, and a continuous fortification between the Firth of Forth and the Firth of Clyde known as the Antonine Wall, built in the second century AD. Beyond Roman influence, there is evidence of wheelhouses and underground souterrains. After the departure of the Romans there were a series of nucleated hill forts, often utilising major geographical features, as at Dunadd and Dunbarton. Castles arrived in Scotland with the introduction of feudalism in the twelfth century. Initially these were wooden motte-and-bailey constructions, but many were replaced by stone castles with a high curtain wall. In the late Middle Ages new castles were