The tomb for the original builders of Stonehenge could have been unearthed by an excavation at a site in Wales.
The Carn Menyn site in the Preseli Hills is where the bluestones used to construct the first stone phase of the henge were quarried in 2300BC.
Organic material from the site will be radiocarbon dated, but it is thought any remains have already been removed.
Archaeologists believe this could prove a conclusive link between the site and Stonehenge.
The remains of a ceremonial monument were found with a bank that appears to have a pair of standing stones embedded in it.
The bluestones at the earliest phase of Stonehenge - also set in pairs - give a direct architectural link from the iconic site to this newly discovered henge-like monument in Wales.
The tomb, which is a passage cairn - a style typical of Neolithic burial monument - was placed over this henge.
The link between the Welsh site and Stonehenge was first suggested by the geologist Herbert Thomas in 1923.
This was confirmed in 2008 when permission was granted to excavate inside the stone circle for the first time in about 50 years.
The bluestones were transported from the hills over 150 miles (240km) to the plain in Wiltshire to create Stonehenge, the best known of all Britain's prehistoric monuments.
Two of the leading experts on Stonehenge, Prof Geoff Wainwright and Prof Timothy Darvill, have been leading the project at Carn Menyn.
They are now excavating at the site of a robbed-out Neolithic tomb, built right next to the original quarry.
They knew that the tomb had been disturbed previously, so rather than excavate inside, they placed their small trench along its outer edge.
Prof Darvill said: "It's a little piece of keyhole surgery into an important monument, but it has actually lived up to our expectations perfectly."
The area has many springs, which may have been associated with ritual healing in prehistoric times - and their existence may be the reason why these particular stones were quarried for another monument so far away.
Prof Wainwright said: "The important thing is that we have a ceremonial monument here that is earlier than the passage grave.
"We have obviously got a very important person who may have been responsible for the impetus for these stones to be transported.
"It can be compared directly with the first Stonehenge, so for the first time we have a direct link between Carn Menyn - where the bluestones came from - and Stonehenge, in the form of this ceremonial monument."
A new series of BBC Two's Digging for Britain begins at 21:00 on Friday, 9 September.