Gas pipe upgrade to reveal secrets of the Old Town

Scotland Gas Networks (SGN) will carry out £420,000 worth of work to upgrade the gas mains on Johnston Terrace and Lawnmarket.

The “essential” work will take around 15 weeks to complete and involves replacing 1050 metres of ageing iron mains with polyethylene ones.

Edinburgh archaeologist Gordon Ewart, who will accompany a team of engineers, said he was confident that a range of artefacts – possibly from early medieval times – would be discovered when the work gets under way next month.

The 59-year-old, who lives in Murrayfield, said: “There are four areas of interest. The first is Johnston Terrace, where the Flodden Wall ran up towards the Castle. The trench will cut across the line at the Flodden Wall. The wall itself sat on top of earlier defensive lines, which could go back as far as the 12th century.”

Mr Ewart, who runs Kirkdale Archaeology in Edinburgh, said engineers would also be digging on the site of the former mansion owned by the Duke of Gordon in the 17th Century.

He added: “There’s a famous map of Edinburgh dated to 1647, which shows all the strange little streets and courtyards off the High Street and around Holyrood and the Castle. We will look at that map to pick up evidence of this early housing. We will be looking at the old pattern of streets in medieval Edinburgh.”

As part of the excavation, which will be 1.5 metres deep, Mr Ewart will also be looking at the site of the former townhouses which stood on the High Street in the 17th century.

“Finally, the last thing we will pick up will be the Weigh House,” he added. “It sat in the middle of the High Street and was a big municipal building, where goods of various sorts were weighed to ensure there were standardised weights and measures. It was demolished in 1822.”

The work will be carried out by Turriff in two phases, and will involve road closures and parking suspensions.

Phase one, from Johnston Terrace to Lawnmarket, will see parking suspended on both sides of Johnston Terrace.

Phase two, from Lawnmarket to George IV Bridge, will mean access to the Lawnmarket from the bridge will be closed.

Access will be provided from Johnston Terrace. Parking in the Lawnmarket will also be affected during phase two, with diversions signposted.

Access for pedestrians will be maintained at all times and all shops and businesses will be open as usual.

Mr Ewart said the work may also uncover evidence of the municipal water supply.

He said: “Two examples of these old wellheads survive. There’s a 17th century well at the foot of the West Bow and another one outside the John Knox House. They were part of the integrated water supply system in the city in the 17th century. We might find evidence of this pipework.”

Director of Operations at Scotland Gas Networks, John Lobban, said: “We have been working with the City of Edinburgh Council, Historic Scotland, Lothian Buses and archaeologists on this major project.

“This project shows that vital work can be carried out with care in historic areas, and we are fascinated by what our archaeologist might find lurking beneath some of the city’s most ancient and mysterious streets.”

Mr Ewart added: “We will find remains of parts of the medieval city, its defences and its houses from top people to ordinary people, from at least the middle of the 16th century to the middle of the 19th or 20th century.”