Marden Henge was once a 45ft high mound surrounded by a water filled ditch which was used for sacrificial offerings.
Although the henge no longer has its vast stone circle it has a large puzzling sunken circular feature which is almost unheard of at Neolithic sites.
A team of 15 archaeologists and historians believe the dig could show the ancient site is even more significant than both Stonehenge and Avebury stone circles.
Archaeologist Jim Leary, 34, said: 'Virtually nothing is known about this vast circle. We are starting from point zero.
'Marden Henge deserves to be understood more partly because of its size, but also due to its proximity to the more famous stone circles at Avebury and Stonehenge.
'The relationship between the latter two sites - chronology of their construction, whether it is built by the same people, how they were used, is of immense interest.
'How Marden relates to them is another layer of interest which we want to study.
'We are potentially looking at a much more intricate system of Neolithic ritual sites in this part of the world than we previously thought.
'The study of prehistory is entering a very exciting phase with lots of fascinating research and dating techniques emerging.
'The stunning discovery of Neolithic houses at Durrington Walls near Stonehenge a few years' ago, for example, has really turned things on its head.
'We certainly hope that this excavation will bring more pieces of the puzzle to light.'