Historians generally agree that the Scottish city of Perth has a name deriving from a Pictish word pert meaning a copse or wood. The antiquity of this name is less clear and is a matter of some debate, as is the question of where the original settlement called Pert was located. Did the city begin as a small trading village on the bank of the River Tay, with a seasonal market frequented by Vikings? Did it develop around an ancient Christian site in the vicinity of the present-day Saint John’s Kirk? Or was the ancestor of Perth originally a Pictish ceremonial centre near the Roman fort a mile or so further upstream where the Tay meets the River Almond?
The earliest record of the place-name Perth or Pert occurs in the 12th century when the town was named among property granted to Dunfermline Abbey in a royal charter of King David I of Scotland. In the following century the place-name appears in the variant form Berth or Bert. This variant was subsequently borrowed by medieval Scottish historians such as John of Fordun and Walter Bower as the basis of a fictional name for the Roman fort at the mouth of the Almond. In their chronicles they called the fort Bertha, a name invented by them because they did not know the Roman name for the place. This name has since stuck and the fort is often marked on maps in a way that could fool the unwary into believing that Bertha was what the Romans called it. The original Roman name was probably Tamia, derived from a native name for the River Tay. In early medieval times, when the long-abandoned site was still used for ceremonial or other purposes by Pictish and Gaelic kings, its name was Rathinveramon (Fort at the mouth of the River Almond). Perth, then, means ‘copse’ or ‘wood’ in the old Pictish language (which was a Celtic language related to the ancestor of Welsh). Bertha is a medieval variant of Perth and was erroneously applied to the nearby Roman fort. The interesting point about Perth’s early name is that it pushes the date of the original settlement backwards into the Pictish period, thereby making the city’s origins far older than the time of its elevation to town status in the 12th century.
M. Hall, H. Hall & G. Cook, “What’s cooking? New radiocarbon dates from the earliest phases of the Perth High Street excavations and the question of Perth’s early medieval origin”, Proceedings of the Society of Antiquaries of Scotland, vol.135 (2005), pp.273-285.