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
City Wall and Moat wooden towers. Attackers had to construct bridges from their wooden towers in order to reach the top of the wall, thus exposing themselves to the defenders of the city. Archaeologists have not been able to provide a precise date for the construction of the city wall and its moat, although historical chronicles suggest the 9th century. Both wall and moat were built atop the Phoenician cemetery, and cut across the ruins of the Phoenico-Persian, Hellenistic and Roman residences. In the late 19th century, the city wall and its moat lost their strategic significance. By the early 1900s, the wall had