Humans have marvelled at the majesty of Stonehenge for thousands of years, but the famous landmark's original purpose has remained a mystery.

Now, a new technique has revealed 15 previously unknown Neolithic monuments around the mysterious monument in Wiltshire.

And one archaeologist thinks they could provide evidence that the stone circle was at the heart of a busy heathen processional route over 4,000 years ago.

Archaeologist Vince Gaffney, of the University of Birmingham, is involved in the Stonehenge Hidden Landscapes Project - a four-year collaboration with the Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology in Austria.

The team has conducted the first detailed underground survey of the area surrounding Stonehenge, covering around four square miles (6km), journalist Ed Caesar reported for Smithsonian.

They discovered evidence of 15 unknown and poorly-understood late Neolithic monuments, including other henges, barrows, pits and ditches, which could all harbour valuable information about the prehistoric site.

In the summer of 2009, geophysicists used magnetic sensors and ground-penetrating radar to scan the area around Stonehenge, detecting unknown structures.

The sensors let experts detect evidence of ancient digging and buildings by mapping variations in the Earth's magnetic field.

'This is among the most important landscapes, and probably the most studied landscape, in the world,' Professor Gaffney told the magazine.

'And the area has been absolutely transformed by this survey. It won't be the same again.'

Professor Gaffney believes these sites suggest Stonehenge was not an isolated monument in an unspoilt landscape, but that there was lots of human activity nearby.

As long ago as 1620, diggers discovered cattle skulls and burnt coals buried in the centre of the stone circle and around 60 years ago, carbon dating of a piece of charcoal in a pit led scientists to believe that Stonehenge was erected in 2,600BC.

In 2003, Mike Parker Pearson of University College London claimed that the workers who built Stonehenge lived in a nearby settlement of Durrington Walls, after unearthing evidence of huts, tools, and animal bones.

He also said that the stone circle was a cemetery, as well as a religious monument.

In the latest study, which took 120 days spread over four years, the experts created a new map of the Stonehenge landscape.

They included what we think of as Stonehenge, as well as a long strip of land called the Curcus, which ran east to west for around two miles (3km).

It is thought the ditch barrier predates the stone circle by several hundred years.

The Curcus barrows - mass graves - to the south of the Curcus were marked as well as the 15 new finds.

It is hoped their contents will become clear with future excavation.

Historians are not sure what purpose the Curcus served and Professor Gaffney as a 'bloody great barrier to the north of Stonehenge.'

Some experts think it was linked to the passage of the sun and this was supported by new clues.

The team discovered gaps in the ditch including a large break in the northern side to allow people to enter and exit the Curcus.

Professor Gaffney thinks the gaps served as 'channels though the landscape' to enable people to move north and south.

He also found a huge pit at the eastern end of the Curcus, which is today 3ft (1metre) underground.

Because it was large - 14.7ft (4.5metres) in diameter - the team thinks it was used for rituals as a 'marker of some kind'. It is also located on the path of the sunrise on the summer solstice.

'We thought, that's a bit of a coincidence!' Professor Gaffney said.

'That was the point at which we thought, What's at the other end? And there's another pit.

'Two pits, marking the midsummer sunrise and the midsummer solstice, set within a monument that's meant to be something to do with the passage of the sun.'

Professor Gaffney told Mr Caeser that on the longest day of the year, the pits form a triangle with Stonehenge, marking sunrise and sunset.

He thinks they may have had fires burning in them and that the site was designed to be seen in the day and night, especially at sunrise and sunset.

'Increasingly we can see the area around Stonehenge as providing extensive evidence for complex liturgical movement - which we can now understand, largely because we know where things are,' he said.

He also believes the building of Stonehenge was a 'monumentalising' of a procession.