A handful of scraps of charred wood and a little pile of stone chips - finds from the first excavation at Stonehenge in more than 40 years - have added thousands of years to the history of one of the world's most famous prehistoric monuments.

There was no gold or bronze, but to the archaeologists who led the excavation, Professors Tim Darvill and Geoffrey Wainwright, the unlovely heap of finds is real treasure. They are convinced the stone chips are evidence of belief in the healing power of the "bluestones" brought 150 miles from south Wales, which endured long after the monument was thought to have been abandoned.

The magical bluestone, spotted dolerite which when newly quarried is a dark blue speckled with brilliant white stars of quartz, made Stonehenge into the Lourdes of prehistoric Europe, they believe, or as Darvill put it yesterday, "the accident and emergency unit of southern England".

The charcoal fragments also add haunting new evidence to the Stonehenge story. Darvill and Wainwright revealed yesterday, at the Society of Antiquaries in London, that the earliest has been dated to 7,000BC, and the most recent to medieval times, suggesting that the site was already important 4,000 years before the oldest stone circle, and continued to draw visitors for centuries after it was believed to have been abandoned.

Although they concede Stonehenge was probably "multifunctional", possibly also serving as a giant calendar marking the solstices, as well as a site of ancestor worship, they are convinced its true importance came from the modest bluestones, the size of a man or smaller, dwarfed by the awesome sarsens.

Two of the original bluestones were broken, many chipped into fragments, and some survive only as stumps underground after being broken up to serve as healing talismans.

Organic remains, including a few specks of grain and seed, have allowed secure dating for the first time of the bluestone circle: around 2,300BC, three centuries later than previously thought.

The stones were repeatedly moved and rearranged, and the enormous sarsen trilithons added, before the final outer circle of sarsen uprights and lintels was created around 1,900BC, creating the world-famous profile of the monument.

Although the double-decker bus height sarsens are undoubtedly the most impressive, Darvill and Wainwright believe they were essentially an architectural framework for the bluestones, just as towering medieval cathedrals grew over the shrines of saints. The stone comes from only one place, an outcrop of the Preseli hills near Wainwright's home in Pembrokeshire. The crags are full of springs, many still regarded as healing holy wells, and ancient decorated stones prove they were important from prehistoric times.

Their theory, which they said yesterday was borne out by their excavation results, was that they were brought to Stonehenge by stupendous human effort because of the belief in their healing power. They completely dismiss the rival theory that the stones were carried by glaciers. "The one tiny flaw in the theory is that there is absolutely no evidence for glaciation of Wiltshire," Wainwright said.

By re-examining old records they have now found evidence of chips of bluestone buried with many bodies in the Stonehenge area - including that of the Amesbury Archer, one of the richest finds in decades, who died around 2,300BC - and they believe further research will uncover many more.

Bluestone fragments have also been found at other monuments, including the summit of nearby Silbury Hill.

Many of the bodies bear the marks of horrible illness or injury, supporting the theory that they came to Stonehenge in futile search of a cure or at least respite from excruciating pain.

The Archer, whose grave was found in 2002 just three miles from Stonehenge, came like the much younger man buried near him - who may have been a son or nephew - from modern Switzerland. The skeleton suggests he spent years in agony from a shattered kneecap, and may eventually have died poisoned by an abscess which rotted a hole through his jaw.

Archaeologists had believed that by the time the Romans arrived in Britain, Stonehenge was just a towering enigma, its ritual importance entirely forgotten.

The latest finds imply a much more complex story: they include a Roman coin among stone fragments, suggesting the Romans also believed in and sought out the healing magic. The later charcoal deposits suggest to Darvill and Wainwright annual gatherings, perhaps for feasting and ceremony at the winter solstice, continuing as late as the 17th century.

The modern-day druids and pagans who assemble bearing green boughs for the winter and summer solstices may not be so far off the mark after all.

The last excavation at Stonehenge was in 1964. Although in April Darvill and Wainwright only won permission from English Heritage for a trench the size of a large hearthrug - "a little piece of keyhole surgery" as Darvill described it - it was the first excavation at which the whole armoury of modern scientific archaeology could be fired. "This is very much work in progress," Wainwright said yesterday. "There are more surprises to come, I'm sure of that."

Next season they will be back in Preseli, looking for more evidence of ritual practice at the home of the bluestones.

"I'm sure we'll find the Welsh architect of Stonehenge yet," Wainwright said.

The excavation was funded by BBC Timewatch and Smithsonian Networks and a documentary on the findings will be screened on BBC2 at 8pm on Saturday.

Theories

The 20th-century archaeologist Jacquetta Hawkes said each generation "has the Stonehenge it deserves - or desires". These are some of the explanations for one of the most spectacular monuments of the ancient world.

· Geoffrey of Monmouth, 12th-century historian, said giants originally brought the stones from Africa to Ireland, where they were used for healing, and then Merlin brought them to Britain.

· John Aubrey, 17th-century antiquary, discovered the row of barely visible pits now named after him, which possibly held the first wooden posts, and believed the structure was a druid temple.

· John Wood the Elder, 18th-century architect, carried out the first accurate survey of Stonehenge in 1740, which directly influenced his designs for the Circus in Bath.

· William Stukeley, 18th-century antiquary, working with the astronomer Edmund Halley, said Stonehenge was completed in 460BC, and was aligned with magnetic north.

· Joseph Norman Lockyer, scientist and astronomer, suggested in 1906 that Stonehenge was a giant astronomical observatory.

· Gerald Hawkins, British astronomer, suggested in 1966, in Stonehenge Decoded, that the monument was a prehistoric computer, capable of complex predictions of planetary alignments and eclipses.

· This article was amended on Wednesday September 24 2008. Our geology was awry in the article above about Stonehenge. The bluestones at the site are spotted dolerite, a blue-grey igneous rock, not dolomite, which is a sedimentary rock resembling limestone. This has been corrected.