The Luas electricity sub-station due for construction in Lower O'Connell Street, Dublin, is to be relocated northwards by three metres to preserve the remains of a 17th-century stable found on the site.
A spokesman for the Railway Procurement Agency (RPA) said yesterday the brick-and-stone structure unearthed during an archaeological excavation would be preserved in situ under the street's central median.
The discovery - made by Mr Franc Myles, of Margaret Gowen and Company, consultant archaeologists on the Luas project - comprises brick walls of a stable and part of the cobbled wall of its adjoining garden.
Located less than 20 metres from the O'Connell monument, this remnant of old Dublin is almost three metres below the existing street level and long pre-dates the extension of Sackville Mall southwards to the River Liffey.
To the north of it was an alley known as Drogheda Street, all of which was later demolished by the Wide Streets Commissioners.
"It would seem that the buildings were collapsed into the ground to raise the street level," Mr Myles explained.
He said the find had once again confirmed the almost pinpoint accuracy of John Rocque's 1756 map of Dublin.
"What a guy! The detail in his map is amazing, even to the extent of showing dung heaps just off Grafton Street ."
But Mr Myles said Rocque, who is better known for his contemporaneous map of London, may have visited Dublin only very briefly and that most of his detailed cartography of the emerging Georgian city was done by assistants.
"These buildings were on the Lotts, which at that time extended eastwards to here, and they're depicted as a type of mews," Mr Myles said, pointing to the map. "Directly adjoining it is what we believe was the cobbled surface of the Lotts."
The excavation is being carried out beneath two trees just north of the O'Connell monument, which appear to date from the 1970s. "There was talk of getting rid of the trees, but now they're staying and we're not going back any further", Mr Myles said.
Dúchas, the Heritage Service of the Department of the Environment, visited the site yesterday "with a view to making a full assessment and working with all the interested parties to resolving the matter".
That was before the RPA decided to move the sub-station.
The RPA spokesman said the sub-station, which measures 30 metres by 10, would be constructed entirely underground and would have no visible impact on O'Connell Street.
"We're moving it north by three metres to preserve the archaeology," he added.
