Media playback is unsupported on your device Media caption The new "henge" is about 900m (2,950ft) from the giant stones

Archaeologists have discovered a second henge at Stonehenge, described as the most exciting find there in 50 years.

The circular ditch surrounding a smaller circle of deep pits about a metre (3ft) wide has been unearthed at the world-famous site in Wiltshire.

Archaeologists conducting a multi-million pound study believe timber posts were in the pits.

Project leader Professor Vince Gaffney, from the University of Birmingham, said the discovery was "exceptional".

The new "henge" - which means a circular monument dating to Neolithic and Bronze Ages - is situated about 900m (2,950ft) from the giant stones on Salisbury Plain.

It's a timber equivalent to Stonehenge Professor Vince Gaffney, University of Birmingham

Images show it has two entrances on the north-east and south-west sides and inside the circle is a burial mound on top which appeared much later, Professor Gaffney said.

"You seem to have a large-ditched feature, but it seems to be made of individual scoops rather than just a straight trench," he said.

"When we looked a bit more closely, we then realised there was a ring of pits about a metre wide going all the way around the edge.

"When you see that as an archaeologist, you just looked at it and thought, 'that's a henge monument' - it's a timber equivalent to Stonehenge.

"From the general shape, we would guess it dates backs to about the time when Stonehenge was emerging at its most complex.

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

Image caption Archaeologists say the find is "exceptional" Archaeologists say the find is "exceptional" Discovering the henge

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

Other wooden structures have been found in the area, one of these being Durrington Walls about 3km (1.86 miles) to the north east of the stones.

Data from the site is being collected as part of a virtual excavation to see what the area looked like when Stonehenge was built.

Speculation as to why the 4,500-year-old landmark was built will continue for years to come, but various experts believe it was a cemetery for 500 years, from the point of its inception.

In 2008, the first excavation in nearly half a century was carried out at the iconic site on Salisbury Plain.

This latest project 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.

Professor Gaffney said he was "certain" they would make further discoveries as 90% of the landscape around the giant stones was "terra incognita" - an unexplored region.

"The presumption was this was just an empty field - now you've got a major ceremonial monument looking at Stonehenge," he said.