A succession of kings held court at Old Roxburgh, or Rokesburg as it was then called, and the Royal burgh by the banks of the Tweed became the largest wool trading centre in Europe. Rokesburg vied with Edinburgh, Stirling and Berwick as the kingdom’s most influential place.
But while the other three settlements have survived, almost nothing remains of Old Roxburgh above ground level.
The burgh, which was granted its Royal charter by King David I in the 12th century, was destroyed and abandoned during the militarisation of the Border in 1460.
Some historians say the land where Rokesburg once stood, on a peninsula near Kelso at the junction of the River Teviot and the Tweed, is Scotland’s most important unexcavated medieval site because it has never been built on. It is understood the programme’s archaeologists made significant discoveries, and it has been suggested more expert work should be carried out.
A Time Team spokesman said: "While Edinburgh, Stirling and Berwick all thrived, Old Roxburgh simply vanished. There are plenty of documents but only a ruined castle remains as a clue to the town’s layout."
Ancient papers, some owned by the Duke of Roxburghe, whose home at Floors Castle overlooks the site, suggest a wide range of tradesmen, including goldsmiths and silversmiths, was working in the area in the burgh’s heyday.
The castle often found itself under English control as the warring armies held the fortifications in turn. At certain points, the burgh’s citizens considered themselves English rather than Scottish. Records show that the burgesses petitioned King Edward II to build a wall round the town "to save us from the brigand Wallace".
Walter Elliot, a Borders historian who worked with the Time Team, said: "Viewers will be very impressed because although the dig was completed in three days, it yielded a tremendous amount of information.
"Previous finds of coins and aerial photographs of the site had suggested there was a complex of linked towns by the riverside. The project set out to establish whether the claims made for Old Roxburgh can be justified"
• Scotland’s Forgotten Capital will be screened at 5pm tomorrow.