"Ancient Scotland, then occupied by Celtic settlers, never became part of the Roman empire, in spite of being invaded on what is now accepted as four, rather than three, occasions. The northernmost frontier of the empire was fortified for only a few years after the battle of Mons Graupius in AD 84, when the Caledonians were defeated by Gnaeus Julius Agricola. An alternative frontier, represented by the elaborate defences of the Antonine Wall, was built in about 142. It was maintained hardly longer than 25 years, and by 180 the Roman invaders had retreated back to Hadrian's Wall. After further Celtic activity, a temporary truce was negotiated personally by the emperor Septimius Severus in 209. Thereafter, until their empire began to collapse, the Romans maintained a fragile hold on Hadrian's Wall in the face of furious attacks by marauding Picts and Scots, and a combined operation by land and sea in 367 against the whole of Roman Britain, by the northern Celts in an alliance with the Franks and Saxons."--Jacket.