The summer solstice on June 21, when the sun climbs to its highest point and daylight lasts longest, is traditionally the day to celebrate midsummer in Britain.
For some it evokes images of modern-day druids greeting the dawn at Stonehenge, the ancient stone circle on Salisbury Plain, in England.
It is uncertain exactly why such stone circles were built or what purpose they served, although most act as giant sundials and astronomical clocks with stones positioned to mark days like the summer solstice.
There are more than 1,000 prehistoric stone circles in Britain and Ireland.
There is no comprehensive blueprint for them; they vary in size, shape, number of stones, style, and orientation. Stonehenge is the only circle built of stones not from the local area.
What is known is that between 3300 and 900 B.C. there were three phases of stone-circle building.
During the first phase, before 3000 B.C., impressive circles, more than 30 meters (33 yards) across, were built on hillsides around the Irish Sea.
They usually had one wider gap to serve as an entrance. Sometimes they had one single standing stone outside the ring, like a signpost proclaiming the land was occupied.
Many perfectly constructed rings of stones were created around 2600 B.C., perhaps because metal was then available. These include the circles of Stanton Drew, in Somerset, and the Ring of Brodgar, in the Orkneys, each more than 90 metres (98 yards) across.
Certain areas seemed to adopt a preferred number of stones. They show a wide range of styles, from plain and concentric rings to rings with avenues, like that at Avebury.
From 2000 to 900 B.C., the tradition of building stone circles declined. By 900 B.C. stone circles, including Stonehenge, were abandoned.
In more recent history, according to folklore, there were numerous traditions of bonfires set ablaze on hilltops on midsummer eve.