Archeologists are assessing damage to a 4,000-year-old prehistoric site on the Mendip Hills.
English Heritage experts have been investigating claims that one of the four Priddy Circles, which are Scheduled Ancient Monuments, has been obliterated.
The Ancient Monuments and Archaeological Areas Act 1979 makes it a criminal offence to destroy or damage a scheduled monument including agriculture, forestry, flooding and tipping.
Land near the circles appears to have been recently re-seeded and tree saplings have been planted close by.
Anyone who damages an ancient monument can be fined.
English Heritage has refused to be drawn on the extent of the alleged damage at this stage.
An English Heritage spokesman would only say: "We are currently investigating reports of damage to the Priddy Circles – a series of four large Neolithic henge monuments in Somerset."
All other interested groups, including Somerset County Council and the Area of Outstanding Natural Beauty, have directed inquiries to English Heritage.
Priddy Circles are an arrangement of four circular earthwork enclosures near Priddy.
The circles are described as 'probable Neolithic ritual or ceremonial monuments similar to a henge'.
The circles, each nearly 200m across, are best seen from the air.
The damaged circle was the most clearly defined of the four.
The total arrangement is spread over roughly 1.2km.
The B3135 cut through the circles and follows the course of the Roman road which runs between Charterhouse and Old Sarum.
Excavations carried out between 1956 and 1959 by members of the University of Bristol Spelaeological Society showed that the banks had stone cores with post and stake holes on either side.
Geophysical surveys in 1995 and a magnetometer survey in 2006 explored the make up of the circles.
They are probably Neolithic ritual or ceremonial monuments similar to a henge.
The external rather than internal ditches makes them unique in Britain.
Although no dating evidence has been found, they appear to be contemporary with Stonehenge.
The circles are the most important surviving Neolithic sites in Somerset.