The discovery of the timber henge just metres from its giant stone double has been hailed as the most exciting find the site in 50 years.

Archaeologists conducting a multi-million pound study unearthed a circular ditch surrounding a smaller circle of deep pits about a metre wide, which are thought to have once been filled by timber posts.

The new henge, which means a circular monument dating back to the Neolithic and Bronze ages, was found just 900 metres (2,950ft) from the stone circle on Salisbury Plain.

Archaeologists believe it was constructed at the same time as Stonehenge was being completed – around 4,500 years ago.

The timber ring has two entrances on the north-east and south-west sides and surrounds an ancient burial mound, which is thought to have appeared much later.

Data from the site is being collected in order to build a virtual picture of what the area looked like at the time Stonehenge was built.

Opinion is divided as to why the ancient landmark was constructed, but many experts believe it was a used as a cemetery for the first 500 years.

A British academic claimed last year that the site had been used as a dance arena for listening to “trance-style” music.

Professor Vince Gaffney, the archaeologist from the University of Birmingham who is leading the dig, said he was “certain” that further discoveries would be made as 90 per cent of the land around Stonehenge has never been excavated.

“The presumption was this was just an empty field – now you’ve got a major ceremonial monument looking at Stonehenge,” he said.

“This is probably the first major ceremonial monument that has been found in the past 50 years or so.

“This is really quite interesting and exceptional, it starts to give us a different perspective of the landscape.”

The excavation is being funded by the Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology, in Vienna, and the University of Birmingham, and is assisted by the National Trust and English Heritage.