Come the dawn of midsummer on 21 June, members of the public can try to tap into the magic for the first time in 15 years.

Gatecrashers disrupted celebrations last year

About 10,000 people - curious tourists, New Age revellers and pagan worshippers - are expected to mark the summer solstice at sunrise, free to wander in and around the stones.

English Heritage banned solstice celebrations in 1985, and later threw up a perimeter fence crowned with barbed wire, following a nasty showdown between riot police and revellers.

The demonstrators had taken exception to the National Trust injunction to stop a free festival in and around the World Heritage Site.

Conflict over the issue intensified and led to the Battle of the Beanfield a few miles from Stonehenge. Seven hundred people were arrested but protesters condemned what they said was police brutality.

Trouble also brewed at last year's invitation-only event, when gatecrashers clambered onto the stones.

Secrets of the ancients

What is it about this 5,000-year-old ring of moss-covered stones with a scenic view of the A303 that exerts such strange pulling power?

Theories abound

Is Stonehenge a temple? A calendar? A burial ground? A weather forecasting station?

Perhaps it is the mystery that shrouds the origins of the monument.

It remains unclear to this day for what purpose the stones were erected on Salisbury Plain - was Stonehenge intended to be a temple, a burial ground or a calendar?

Almost the only common belief among Stonehenge scholars is that the stones are aligned with both the winter and summer solstices.

When the midsummer sun rises directly over the heel stone, it marks the turning of the season and the approaching harvest season. At midwinter, the sun rises over a stone on the opposite side of the circle.

Haul halted

The site is thought to date back to about 3100BC, when it was little more than a ditch and a circle of round holes cut into the chalk. Cremated human bones have been excavated from the site.

It was abandoned soon after, and left untouched for more than 1,000 years.

Some experts believe bluestones from the Preseli Hills in southwest Wales were heaved 240 miles on sleds and boats to the Wiltshire site in about 2150BC.

Volunteers managed just one mile on their first day

It is this journey that the ill-fated Millennium Stone project has attempted to recreate. The three-tonne stone is now 17m under water off the Pembrokeshire coast after sinking over the weekend.

By 2000BC, sarsen stones were erected, with the largest weighing in at 50 tonnes. Modern calculations show that it would have taken 500 men to pull one stone.

Within 150 years, the bluestones were rearranged in the horseshoe and circle seen today. Originally, there were 60 stones in the circle but many have since crumbled.

The joint chief of the British Druid Order, Greywolf, explains on the order's website why worshippers beat a path to the ancient site.

"Having felt the resonance of the stones responding to the beat of a drum, having heard the voices of our ancestors join in the Awen chant, having seen the priests and priestesses of elder times walk among the stones, I could hardly fail to recognise the power of the place."