WORKMEN digging below Bridgwater's Castle Street stumbled across an "outstanding" piece of the town's medieval history last week, unseen for more than 700 years.
Wessex Water officials were renovating sewers underneath the street on Monday when they unearthed a smugglers tunnel and part of old curtain wall from Bridgwater Castle - leading one archaeologist to proclaim it "one of the most important finds of the 21st Century".
Bridgwater Castle dates back to 1200, where William Briwere built a complex of buildings covering eight acres across parts of present day Kings Square and Castle Street.
The giant structure massed next to the river and included a chapel, a kitchen, a cellar, stables and a dungeon.
Today, only the Water Gate and some walling on the West Quay and in Queen Street survive above ground.
But Wessex water workers made the historic discovery after digging ten feet into the ground at the bottom of Castle Street, while taking part in a major sewer regeneration project.
Heath Hayes, site agent for Wessex Water, said: "We were fully aware of the history here and were working with an archaeologist on site, so we did expect to come across it at some point.
"We had actually dug deep enough yesterday, but the archaeologist asked us if we could extend the hole to show a bit more of the castle, to which we agreed. It's a nice surprise to find something of this age."
Andy Tizzard, the onsite archaeologist from Context One Archaeological Services said the smugglers tunnel would have been used to transport goods from ships coming in on the River Parrett - and the passage was one of several leading to houses in the town.
Mr Tizzard then explained the significance of the find to the Mercury.
He said: "In my 30 years of being an archaeologist this is the first castle wall I know of to be found under a road. It is, in its own right, a quite exceptional find.
"This discovery enables historians to study just how people built a medieval castle in the West Country and this opportunity will never arise again.
"Wessex Water's absolute cooperation and commitment to preservation means we'll be able to document these building techniques as serious, credible evidence.
"I have no doubt that this is a find of national, as well as local, importance."
The excavation and discovery of the medieval wall will be recorded by archaeologists, before the workers finish up and the hole in the ground is sealed.