A skull found by a dog walker in Somerset dates back to the Iron Age, scientists have revealed.
Roger Evans of Newtown found the skull on the banks of the River Sowy in March last year.
Scientists say the head belonged to a woman aged 45 or older in the late Iron Age - 380-190 BC, centuries before the first Roman invasion of Britain.
Further investigations nearby revealed timber posts, which are being tested to see if they are from the same date.
Following the discovery, the Environment Agency (EA) reduced water levels in the area to allow South West Heritage Trust (SWHT) and its own archaeologists to search for more clues.
No more human remains were found but the series of round, timber posts driven into the river bed are thought to have been a remnant of a causeway or raised walkway.
Radio carbon-dating tests are being carried out to find out their age.
Water levels have since been returned to normal to preserve the structures.
Experts believe the Iron Age woman's head had been severed, either at or shortly after her death.
SWHT archaeologist Richard Brunning said: "Severed heads are not an unusual discovery for the Iron Age, but the placement of the skull in a wetland beside a wooden structure is very rare, possibly reflecting a practice of making ritual offerings in watery environments."
Analysis by a human bone expert showed the Iron Age woman had suffered considerably from gum disease and tooth loss.
Her diet included coarse material, which had unevenly worn her remaining teeth and resulted in severe osteoarthritis in the joint of her right jaw.
She had also suffered at least one episode of chronic illness or nutritional stress during childhood.