The intriguing history of Stonehenge

Stonehenge was built in several phases over more than 1,500 years that started around 3100 BC in the Neolithic period. 

The earliest structure probably included a circular 'henge' ditch and bank. 

During the earliest phase of Stonehenge, the builders created the 'Aubrey Holes': 56 pits dug inside the ditch. 

Because of this, researchers think that the site and the pits were used for ceremonial purposes. 

Further digs have shown that Stonehenge was also used as a burial place during its earliest phase, with human remains that date from around 3000 BC found in the circular ditch.

One of the most puzzling parts of the site is the ancient 'Avenue' processional path that links Stonehenge with the River Avon. 

It is nearly 3 kilometres (1.9 miles) long and was made during the Stonehenge 3 period, between 2600 and 1700 BCE, and it lines up with the sunrise of the summer solstice, which suggests its use for ceremonial or ritual purposes. 

The Avenue has a pair of parallel banks about 34 metres (112 feet) apart with outer ditches. 

It starts near the River Avon and runs north-northwest for about 1 kilometre (0.62 miles) before it turns west and finally reaches the northeast entrance of Stonehenge.

The first smaller stones arrived at the site around 2600 to 2500 BC. 

The bluestones were moved more than 150 miles (240 kilometres) from the Preseli Hills in Wales and were set in a double circle inside the existing earthwork enclosure. 

The bluestones may have been carried to Stonehenge along the Avenue, where builders used a mix of log rollers and rivers. 

However, it is not entirely clear why these stones were brought to the site. 

There is some evidence that they could have been used for their sound properties and possibly for ritual purposes.

Stonehenge went through a series of different changes over time when the original bluestone circle was rearranged at one point. 

Then a larger circle of sarsen stones was added. Such sarsen stones, up to 30 feet tall and 25 tons, were brought from the West Woods near Marlborough Downs, about 15 miles (25 km) north of the site. 

They form the famous later-erected, 2500 to 2400 BC outer circle and trilithons, and they use mortise and tenon joints to hold the lintels on top of the uprights. 

One of the most well-known sarsen stones, the entrance-side Heel Stone, stands outside the Stonehenge earthwork. 

It is a single, huge block that stands within the Avenue, roughly 77.4 metres (254 feet) from the centre of the Stonehenge circle. 

The stone is 2.4 metres (7.9 feet) thick with a height of about 4.7 metres (15.4 feet) above ground, and another 1.2 metres (3.9 feet) lies buried below the surface.

When the Beaker People arrived in the area around 2500 BC, European Beaker migrants brought bell-form pottery with them that had reached Britain through large-scale migration. 

Genetic studies have shown that the arrival of the Beaker People led to a near-complete replacement of the earlier Neolithic population in Britain, causing a 90% change in the genetic make-up of the population. 

Associated Beaker migration introduced new technologies and practices, including metalworking, and marked the change from the Neolithic to the Early Bronze Age. 

The Beaker People added a series of earthen mounds to the site that are thought to have been used as burial sites for important members of their community.

After 1500 BC, Stonehenge saw little change, and the monument's active building phases largely ended around this time. 

The last known building activities involved the digging of the Y and Z Holes around 1600 BC. 

Such holes were likely meant for more stones, but they were never filled.

One of the most interesting things about Stonehenge is its alignment with the summer and winter solstices. 

People who stand inside the stone circle can watch the sun rise over the Heel Stone during the solstice. 

However, much of what we think we know about Stonehenge depends only on archaeological findings because no one wrote down its history. 

Because there is a lot we can never know, over the years, people have imagined many different legends to help explain the monument. 

For example, in the 12th century, the writer Geoffrey of Monmouth said that the Arthurian wizard Merlin built the monument. 

Other legends say that giants brought the stones to the site or that aliens moved them.

In more recent times, Stonehenge has been linked to Druidic practices, and it has become a place for modern-day pagans to meet and celebrate the solstices and equinoxes. 

A more believable theory was suggested by archaeologists Geoffrey Wainwright and Timothy Darvill in 2008 when they proposed that Stonehenge may have functioned as a healing centre, based on human remains that show signs of injury and illness. 

Whatever its original purpose, today Stonehenge, one of the most popular tourist spots in the UK, attracts more than 1.5 million visitors each year because people visit for many reasons, including all the ones listed above.

In recent times, people have tried to gather as much solid evidence about the site as they can. 

Earlier, 17th-century historian John Aubrey was one of the first to study Stonehenge in detail and is known for finding the circle of pits that are now called the Aubrey Holes. 

Then, in the early 18th century, the historian William Stukeley surveyed the site, created a detailed map, and suggested that Stonehenge was a temple of the Druids. 

In the early 20th century, parts of Stonehenge were restored, with several stones put back upright to stop them from falling and to keep the structure for future generations. 

It wasn't until 1986 that Stonehenge was finally named a UNESCO World Heritage Site because of its importance to Britain.

In 2015, a team of archaeologists who used high-tech sensors during a project between the University of Birmingham and the Vienna-based Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology discovered evidence of a large stone circle called a 'superhenge' or Durrington Walls about 2 miles (about 3.2 kilometres) from Stonehenge. 

It is one of the largest known henge monuments in Britain, with a diameter of about 500 metres (about 1,640 feet). 

Durrington Walls consisted of 90 stones that stood upright, some originally 4.5 metres (about 15 feet) tall, that had been buried under a bank of earth for thousands of years. 

It is thought to have been a settlement or meeting place, possibly for Stonehenge builders or users, because excavations have revealed evidence of houses and feasting, which suggests it was a lively community space. 

The closeness and alignment with Durrington Walls made archaeologist Mike Parker Pearson suggest that Stonehenge was part of a wider area linked to rituals of life and death that connected the living at Durrington Walls with the ancestors at Stonehenge.