The stones are thought to have been placed at the site in about 1500BC
The discovery of stones that are thought to date back to the Bronze Age have halted a multi-million pound sewage treatment project in Cornwall.
South West Water has stopped work while Cornwall Council's archaeologists investigate the site at Trevalga, which lies between Boscastle and Tintagel.
The stones encircle a dark circular stain in the ground and are thought to denote the location of a round house.
Archaeologists believe the site could date back to about 1500BC.
Senior archaeologist Andy Jones said his team was hoping to find traces of people's daily lives through controlled excavations of the site over the next few weeks.
"Most of what we will find will probably be shards of pottery and maybe work stone implements," he said.
"There is a dark, circular stain with darker soil in the middle of it and around the periphery there are smaller stones where the wall would have been around the edge of it.
"Based on its form, it's looking like it's Bronze Age - probably Middle Bronze Age."
According to Mr Jones such discoveries are relatively frequent across the county.
"We have excavated between 20 to 30 of these sites so it's giving us a chance to flash out the pattern of settlement in lowland Cornwall," he said.
"Of course on the moors they are exceptionally common because there hasn't been later agriculture so on Bodmin Moor there are hundreds of them scattered about."
The discovery was made when a top layer of soil was removed as part of work to build a sewage treatment works and five pumping stations which will be connected to each other via five miles (8km) of sewers.
Ian Lake from South West Water said: "There will potentially be a slight delay to the programme but inevitably with any programme planning there are contingencies built into that.
"We are in the hands of the archaeologists to tell us as and when it's suitable for us to continue."