To the west of the town there is an ancient earthwork known as the Picts' Work Ditch or Catrail. It extends many miles south and its height and width vary. There is no agreement about the purpose of the earthwork. There is another ancient site on the north-western edge of the town, at Torwoodlee, an Iron Age hill fort, with a later Broch known as Torwoodlee Broch built in the western quarter of the hill fort, and overlapping some of the defensive ditches of the original fort. The Romans destroyed the broch in AD 140, soon after it was completed.