A stone circle is a circular alignment of standing stones. They are commonly found across Northern Europe and Great Britain and typically date from the Late Neolithic and Early Bronze Age eras, with most concentrations appearing from 3000 BC. The best known examples include those at the henge monument at Avebury, the Rollright Stones and elements within the ring of standing stones at Stonehenge. Ancient stone circles appear throughout Europe with many appearing in the Pyrenees, on the Causse de Blandas in southern France in the Cevennes, in the Alps, and Bulgaria.Northern Ireland: A stone circle is a circular alignment of standing stones. They are commonly found across Northern Europe and Great Britain and typically date from the Late Neolithic and Early Bronze Age eras, with most concentrations appearing from 3000 BC. The best known examples include those at the henge monument at Avebury, the Rollright Stones and elements within the ring of standing stones at Stonehenge. Ancient stone circles appear throughout Europe with many appearing in the Pyrenees, on the Causse de Blandas in southern France in the Cevennes, in the Alps, and Bulgaria. Stone circles are usually grouped in terms of the shape and size of the stones, the span of their radius and their population within the local area. Although many theories have been advance to explain their use, usually around providing a setting for ceremony or ritual, there is no consensus among archaeologists as to their intended function. Their construction often involved considerable communal effort, including specialist tasks such as planning, quarrying, transportation, laying the foundation trenches, and final construction. There is growing evidence that megalithic constructions began as early as 5000 BCE in northwestern France, and that the custom and techniques spread via sea routes throughout Europe and the Mediterranean region from there. The Carnac Stones in France are estimated to have been built around 4500 BCE and many of the formations include megalithic stone circles. The earliest stone circles in England were erected 2500-3000 BCE during the Middle Neolithic (c. 3700–2500 BCE). Around that time stone circles began to appear in coastal and lowland areas towards the north of the United Kingdom. The Langdale axe industry in the Lake District appears to have been an important early centre for circle building, perhaps because of its economic power. Many had closely set stones, perhaps similar to the earth banks of henges, others were made from unfounded boulders rather than standing stones. Recent research shows that two oldest stone circles in Britain (Stenness and Callanish)were constructed to align with solar and lunar positions. Some sites do not contain evidence of human dwelling. This suggests that stone circles were constructed for ceremonies. The variety of the stones excludes the possibility that they had astronomical observation purposes of any precision. Sometimes a stone circle is found in association with a burial pit or burial chamber, but the great majority of these monuments have no such association. Recumbent stone circles are a variation containing a single large stone placed on its side. The stones are often ordered by height, with the tallest being the portals, with gradually reducing heights around each side of the circle, down to the recumbent stone, which is the lowest. The type is found throughout the British Isles and Brittany, with 71 examples in Scotland, and at least 20 in south west Ireland, including Drombeg stone circle near Rosscarbery, Co. Cork. Scottish recumbent circles are usually flanked by the two largest of the standing stones immediately on either side. These are known as 'flankers'. The stones are commonly graded in height with the lowest stones being diametrically opposite to the tall flankers. It is fairly common for the circle to contain a ring cairn and cremation remains.