The planned construction of a new bypass has led to the discovery of a canoe which is believed to be around 3,500 years old.
The timber canoe was found under the route for the new Caernarfon and Bontnewydd bypass in Gwynedd.
Archaeologists believe the canoe, which was found within a large "burnt mound", is from the Bronze Age and dates back to at least 1,500BC.
The timber was found preserved within a trough underneath the burnt mound, with tests finding that it was made from the trunk of a single oak tree which had been hollowed out.
Experts believe it is likely to be a canoe which was re-used as a trough, although they admit it is possible it was always intended for the function of a trough.
If it is a canoe, archaeologists have said it is an extremely rare discovery and the first prehistoric example to be found in North West Wales.
It is now being examined further by experts, NorthWalesLive reports.
Jenny Emmett, senior planning architect at Gwynedd Archaeological Planning Service, said: “The archaeological mitigation is going very well and the results so far have already added considerably to our knowledge of the area.
"The scheme is expected to continue to add new information as further discoveries emerge, both on site and during the specialist analysis of the remains that will take place following the excavations. "
The experts said burnt mounts were fairly common sites usually found close to water and were generally used to heat water for cooking, bathing, dyeing or leather treatment.
Work at the site has also uncovered a section of roman road, which had previously been identified on a geophysical survey.
The work allowed the investigation of a much longer stretch of the road and has confirmed the route of the road between the forts of Segontium (Caernarfon) and Canovium (Caerhun, Conwy Valley), which was previously uncertain.
An early medieval industrial site which dates to the 8th century has been also uncovered.
Although no traces of metal were found during the excavation, samples collected during an earlier phase of work contained fragments of iron known as hammerscale which are hot sparks that are produced when hot iron is struck by a hammer.
The first phase of planned archaeological studies started in February and has now been completed.
The Welsh Government said the findings do not impact on construction of the Caernarfon and Bontnewydd bypass which remains on schedule and could be completed by autumn 2021.
But there are concerns that the construction of the bypass could affect an historic well dating back hundreds of years.
Ffynnon Fair, which is connected to the nearby church, dates back to the 15th century and was an important source of water for the pilgrimage route between Bangor and Bardsey Island.
In a letter to economy minister Ken Skates, Howard Huws, secretary of Cymdeithas Ffynhonnau Cymru (Welsh Wells Society), said: "By the second of this month it was clear to me that work on the site was endangering the well. You can hardly avoid the huge pile of soil and stone in the adjacent field and the pile of cut down trees thrown around the well.
"Despite this the well continued to flow. Two days later the area had been covered by tons of stone and soil and the only flow visible was through a plastic tube that had been covered.
"I cannot express my sadness from seeing what has been done. Information passed onto the local contact has been ignored."
The Welsh Government said the presence of the well has been considered.
The £135m bypass will take traffic past Caernarfon and Bontnewydd and aims to relieve congestion and improve safety in the area.
Transport Minister Ken Skates said: “The Caernarfon and Bontnewydd bypass is a significant Welsh Government scheme in North West Wales which, when complete, will deliver great benefits for local communities as well as people travelling in the area.
"The archaeological findings are another huge positive to come from this development and provide an exciting and thought-provoking insight into the region’s ancient history."