Scotland during the Roman Empire of the geography of Scotland had extended to the "Hebudes" (The Hebrides), "Dumna" (probably the Outer Hebrides), the Caledonian Forest, and the Caledonians. Ptolemy, possibly drawing on earlier sources of information as well as more contemporary accounts from the Agricolan invasion, identified 18 tribes in Scotland in his "Geography", but many of the names are obscure. His information becomes much less reliable in the north and west, suggesting early Roman knowledge of these area was confined to observations from the sea. Famously, his coördinates place most of Scotland north of Hadrian's Wall bent at a right angle, stretching due eastward
Scotland during the Roman Empire fortification built across the width of what is now northern England. The wall was 80 Roman miles (73.5 statute miles or 117 kilometres) long, its width and height dependent on the construction materials which were available nearby. East of the River Irthing the wall was made from squared stone and measured 3 metres (9.7 ft) wide and 5–6 metres (16–20 ft) high, while west of the river the wall was originally made from turf and measured 6 metres (20 ft) wide and 3.5 metres (11.5 ft) high; it was subsequently rebuilt in stone. The wall was augmented by various ditches,