The remains of two castles, one of which dates back to medieval times, have been discovered by workmen installing a sewage pipe in Glasgow.

Archaeologists say the ruins of 17th century Partick Castle and another structure used by bishops in the 12th or 13th century are the the most significant historic finds in the city for a generation.

Stone walls and various artefacts have been unearthed as Scottish Water installed part of its upgrade to the city's waste water infrastructure.

There is documentary evidence the 17th century castle existed, and that the bishops of Glasgow spent time in what was then rural Partick in the 12th century, but the archaeological discoveries are being described by experts as “the first hard, tangible evidence” that either castle existed.

The site was later used for the old Partick Central railway station, a metal scrapyard and a foundry during the industrial age.

Painstaking excavations also uncovered fragments of pottery, metalwork, leather, glass and animal bones, estimated to have a date range of between the 12th and 17th centuries.

Hugh McBrien, of West of Scotland Archaeology Service (WOSAS), said: "No one knew anything about the 12th century castle in Partick.

"There was documentary evidence that the bishops of Glasgow spent time in Partick and there have been historical references to ‘charters signed at Partick’. But that’s all.

“It has been known that there was a tower house or castle in the 17th century but all we had were antiquarian drawings and documents that refer to Partick Castle.

“So we expected there was archaeology in this area, because of historical records, but this discovery is the first hard, tangible evidence that both castles existed.

“This is the most significant archaeological discovery in Glasgow in a generation.”

The discoveries were made in the Castlebank Street area on the north bank of the River Kelvin, just before it joins the River Clyde.

They took place during preparations for a £3m Scottish Water project to install a new sewer overflow.

Warren Baili, the project manager with Glasgow-based GUARD Archaeology, added: "These findings made during Scottish Water’s work are of national significance and provide a rare glimpse into the medieval beginnings of Partick and Glasgow.

"The survival of these medieval remains is especially remarkable given that the site, not unlike many industrial river banks across Britain, has witnessed such large-scale destructive development over the centuries."

Scottish Water’s upgrade to the area’s waste water infrastructure is the biggest since Victorian times and includes the £100m Shieldhall Tunnel development.