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Revellers take part in incantations during a sunset ceremony as they prepare to celebrate today's summer solstice at Stonehenge REUTERS/Kieran Doherty

Druids, pagans, Christians and tourists are gathering at England's prehistoric Stonehenge site on Salisbury Plain to mark the Summer Solstice.

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Revellers arrive before dawn to celebrate summer solstice at Stonehenge on Salisbury Plain REUTERS/Kieran Doherty

In the Northern Hemisphere 21 June is the day of the year when the sun is above the horizon for longest. The Winter Solstice is on 21 December, when the sun is visible for the shortest time.

The Winter and Summer Solstice are marked in different ways across the world.

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Revellers take photographs as they prepare to celebrate the solstice REUTERS/Kieran Doherty

Worshippers have gathered at Stonehenge for 8,000 years and in recent years there has been a revival as new-age druids and pagans have been joined by travellers, festival-goers and tourists keen to see the ancient stones on this special day.

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The Solstice has been marked for 8,000 years REUTERS/Kieran Doherty

In 1985 the so-called "Battle of the Beanfield" took place between revellers and police determined to prevent them descend on the site en masse. 12 people were hospitalised and 420 arrested. The cause of the confrontation is still disputed.

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Hundreds were arrested or hospitalised in the "Battle of the Beanfield" in 1985 Youtube

Police claimed travellers attempted to run them over in their vans and buses. The travellers claimed police ambushed a peaceful gathering of people.

In the following years there were a number of other confrontations, though none of the scale of 1985, but now the event is relatively peaceful. However police made 25 arrests last night, mostly for drug offences.

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Revellers perform yoga as they celebrate the summer solstice Reuters/Kieran Doherty

English Heritage, which manages the site, is providing what it calls "managed open access" to Stonehenge today. However, visitors are warned that traffic conditions in the area will be heavy and advise anyone interested in attending to consult the English Heritage website.

Tens of thousands of people are expected to attend Stonehenge today as it's the first time for several years the Summer Solstice has fallen on a weekend.