David Miles, former Chief Archaeologist at EH writes: Brochs come at the end of a long tradition of stone house building, including wheel houses. It used to be assumed that they were exotic introductions created by newcomers. Difficult to date but recent evidence from Scatness in Shetland suggests that they are earlier than previously thought. Charred barley in the CONSTRUCTION levels has been radiocarbon dated to between 400 and 200 BC"

Francis Pryor agrees date but claims they were used more for domestic purposes that defensive. Used throughout Late Scottish Iron Age ie up to 900 AD.