Stonehenge may be even older than we think, a new excavation has found. The famous "bluestones" which now form the smallest of the circles may have once stood around its perimeter, centuries earlier.

The new evidence comes from investigation of one of the 56 "Aubrey Holes" (named after the seventeenth-century antiquary who first noted them), which lie just inside the ditch and bank of the original henge monument, constructed in the early third millennium BC. Re-excavation of Aubrey Hole 7, originally dug in 1920, showed a layer of crushed chalk at the bottom that suggested it had once held a heavy stone.

"This had been missed by archaeologists twice before: it seems likely that similar evidence still survives in other Aubrey Holes", said Mike Pitts, one of the excavation directors. "We propose that very early in Stonehenge's history, 56 Welsh bluestones stood in a ring 87 metres (285 feet) across." This early stone circle would date to 3000 BC, seven centuries before Stonehenge reached its present configuration.

"The new evidence from Aubrey Hole 7 suggests megaliths were present throughout Stonehenge's existence" Mr. Pitts said. "Standing stones and burial of the dead may have been prominent aspects of Stonehenge's meaning and purpose for a millennium".

Times Archive, 1921: The mystery of Stonehenge

Magic lore of the builders - old bones and new theories

• A prehistoric racecourse

• Leading article: Stonehenge

• Letter to the editor: Stonehenge

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In the 1950s, when the last Aubrey Hole investigation was carried out, it was suggested that they held a ring of timber uprights, something seen elsewhere, including the nearby site of Durrington Walls and also at Arminghall in Norfolk. Professor Mike Parker Pearson noted, however, that in the 1920s it had been suggested that the bluestones had stood in the holes.

Many of the Aubrey Holes held cremated human remains, and the reason for the dig this August was to recover more bones for analysis; the project was separate from the trench inside the main circle of giant sarsen stones, dug this spring and recently the subject of a BBC Timewatch programme raising the possibility that Stonehenge was an ancient therapeutic centre, as stated in The Times "Now they think Stonehenge was an A&E centre" (September 22, 2008).

The re-evaluation "has sweeping implications for our understanding of Stonehenge", Mr. Pitts said. It means that at the least, the bluestones were transported from Wales at a much earlier date than hitherto accepted, with implications for the organization of Neolithic society in Britain five thousand years ago. Designing a monument using exotic materials, acquiring them and constructing this putative early stone circle argues for social control, and knowledge of distant domains, more complex than we have envisaged.