Archaeologists working on the road at the Tesco site in Newtown
One of the longest sections of Roman road ever found in Wales is being unearthed at the site of a new Tesco.
The highway was carved out of the Powys countryside in Newtown 2,000 years ago, and is thought to have linked two forts.
Archaeologists are excavating three separate sections of the road, and they expect to uncover a total of 300 metres.
The work will not delay the development of the supermarket.
Archaeologists from the Clwyd-Powys Archaeological Trust are working on the site of the town's old Smithfield market, which is being redeveloped as a Tesco store.
Evidence a Roman highway existed was found in December 2006, but archaeologists have only been able to properly excavate it over the last 10 days.
Site director Ian Grant said the road would have been used for troop movements between a legionary fort at Forden, near Welshpool and Caersws, a few miles from Newtown.
Mr Grant said: "This sort of find is extremely rare, especially in Wales.
"We have excavated between 70 and 80m so far and the road is six metres wide.
"We haven't found any Roman artefacts, but the next step is to looks for settlements."
Archaeologists expect to be on site for a minimum of eight weeks.
Mr Grant said the road would eventually be covered by the new store.