BBC News 24's Christine Hussey reports from a druid wedding in Cornwall

It is also the day when you watch the sun rise, while gathered around ancient stones adorned in oak leaves and branches. But then you probably already knew that, presuming you are a Druid.

The summer solstice, or in its Celtic name, "Gorsedd", has long been an important day in the Druid calendar, which marks the various events of the four seasons.

It is even more significant this Sunday because for the first time in a decade, the English Heritage is allowing around 100 Druids to go to Stonehenge to celebrate the marriage of the sun and the earth.

Who on earth?

To many of us, the Druids sound as if they have walked straight out of a science fiction novel, or perhaps even suggest something sinister akin to a strange cult or weird religious sect. But to understand truly who they are, you have to be prepared for a history surrounded by even more fantasy, myth and mystery.

The origins of the Druids were as important figures or "religious professionals" among the Celts, who came to Britain in 1500 BC. In this pre-Christian era, Druids acted as judges, doctors, diviners, mages, mystics, and clerical scholars, in other words, they were the intelligentsia of the time. They knew poetry, philosophy, astronomy and science inside out and were considered the bravest and most wise and respected members of Celtic society.

Another of their important functions, according to Celtic tales and mythologies, was they were able to exhibit a range of magical powers, such as divination and prophesy, healing, levitation, shapechanging and they could even control the weather.

Still practising, the Druids began over 3,000 years ago

This enabled them to play a very useful role in the lives of their respective tribes, for example, advising on policies, announcing the beginning of agricultural seasons and in times of war, their skills were needed to learn about the enemy's plans or to call on the elemental powers to aid the tribe.

There can be no discussion of Druidism however, without noting their fundamental belief in the concept of reincarnation. Druids believe that the soul is immortal and after a person dies, they are transported to the Otherworld, only to come back again in another human body. That is why at every birth, the Celts mourned the death of a person in the Otherworld which had made the new birth possible.

Where are they now?

Amazingly, over 20 centuries later, the Druids still exist, and around 10,000 Druids still practise in Britain. In 1989 the Council of British Druid Orders was formed with just two or three founding member orders, which, according to history and legend, had been in existence for 1,500 years. There are now 12 major orders all over the Britain and the Celtic islands.

Some may put the "re-emergence" of Druidism over the past decade down to the fact that it has once again found a place in time. One reason is the growing interest in the environment and the myths and legends of England, which are linked with the wave of New Age travellers dotted around the British countryside.

Druids and their worship of pagan gods and goddesses from way back in Celtic times have their roots in the exaltation of Mother Earth, the elements and the natural world. The name Druid itself is connected with the Celtic word for "oak tree".

The celebration

Druid orders dotted around the country meet and continue traditions of reading Celtic poetry, while dressed in robes and wearing ancient Celtic symbols. This year they will have the chance again to celebrate the shortest night of the year at their traditional meeting place of Stonehenge.

The Druids believe the mighty oak represents the powerful sun

Stonehenge is much older than Druidism and probably as old as the Troy. Its famous and massive stones stand on an extensive prehistoric landscape that houses the remains of civilisations dating back to the Stone and Bronze Ages.

Some Druids say their religion has marked the summer solstice at Stonehenge for nearly 800 years now, but they - along with everybody else - were banned from worshipping at the ancient site by English Heritage following incidents between police and travellers in 1989.

They have however, continued to celebrate the festival but usually on layby which was within sight of Stonehenge. The Druids can now form their traditional circle around the stones when the sun peeks over the North Sea on Sunday morning, with the conch shell sounding to herald a new dawn and new season.