The stone line is likely to have marked a ritual procession route and is thought to date from the same time as the sarsen circle at Stonehenge.
Archaeologists believe the stones were pushed over and a bank built on top, but they are still trying to work out exactly why they were built. Nothing exists like it in the Neolithic world.
"It's utterly remarkable," said Professor Vince Gaffney, of the University of Bradford.
"It's just enormous. It is definitely one of the largest stone monuments in Europe and is completely unique. We've never seen anything like this in the world.
"We can't tell what the stones are made of, but they are the same height as the sarsens in the Stonehenge circle, so they may be the same kind. It was probably for a ritual of some sort, or it could have marked out an arena. These monuments were very theatrical. This a design to impress and empower.
"Not only does the new evidence demonstrate a completely unexpected phase of monumental architecture at one of the greatest ceremonial sites in prehistoric Europe, the new stone row could well be contemporary with the famous Stonehenge sarsen circle or even earlier."
Durrington Walls, 3km north-east of Stonehenge, is one of the largest known henge monuments, measuring about 500m in diameter and built around 4500 years ago in the Neolithic age. It is surrounded by a ditch of up to 16m wide and a bank of more than 1m high and is built on the same summer solstice alignment as Stonehenge.
Some archaeologists have suggested that the builders of Stonehenge lived at Durrington.
A nearby wooden structure, called Wood Henge was thought to represent the land of the living while Stonehenge was the realm of the dead. But the discovery of the stones suggests that Durrington Walls had a far earlier and less domestic history than has previously been supposed.
The Bradford archaeologists have been working alongside an international team as part of the Stonehenge Hidden Landscapes project, using the latest technology to map the area.
"Everything previously written about the Stonehenge landscape and the ancient monuments within it will need to be rewritten," said Paul Garwood, senior lecturer in archaeology at the University of Birmingham and principle prehistorian on the project.
Dr Nick Snashall, National Trust archaeologist for the Avebury and Stonehenge World Heritage Site, said the new results added "a whole new chapter to the Stonehenge story".