L'époque de construction de ce type de mégalithe est à placer dans la Préhistoire récente avec des dates comprises entre 3500 et 2000 avant J-C.
On ne peut aujourd'hui expliquer précisément la fonction de ce type de monument.
Certains chercheurs avancent l'idée de lieu de rassemblement cultuel tandis que d'autres préfèrent l'idée d'un lieu d'observation des astres ou de la Lune. Certains chercheurs vont jusqu'à postuler qu'ils étaient les marqueurs d'une géométrie ancestrale.
Les cromlechs sont des monuments mégalithiques nettement moins nombreux que les dolmens ou les menhirs qui datent pourtant de la même époque.
En France, les cercles de pierres sont assez peu nombreux dans le sud de la France alors que les dolmens abondent en très grand nombre.
C'est en Bretagne que se trouvent le plus de cromlechs français.
En Europe, les îles Britanniques comptent un nombre très important de cromlechs et notamment celui mondialement connu de Stonehenge et celui de Salisbury.
Un cromlech est un monument mégalithique préhistorique constitué par un alignement de pierres levées (menhirs), formant une enceinte, généralement circulaire ou ovale. Parfois un menhir est placé au centre.
On peut trouver des cromlechs qui ont d'autres formes, depuis le simple alignement droit ou rectangulaire jusqu'aux longues murailles serpentantes, mais on considère qu'il ne s'agit pas de véritables cromlechs.
All experts agree that stone circles are of pre-Christian date, but beyond that stone circles have proven difficult to date accurately. Radiocarbon dating has produced a wide range of dates at different sites. This is at least partly due to an inadequacy of materials suitable for radiocarbon dating that can be reliably obtained from the sites. The diversity of radiocarbon evidence may also suggest that stone circles were constructed over a very long period, or were sometimes reconstructed at later dates. It is often not clear when building started. A further obstacle to dating is that there are generally no other archaeological artifacts associated with the stone circles. 'Traditional' archaeological artifacts, such as pottery shards, bones, etc., are not often found at the sites, and when found are frequently of a later date than the associated stone circle.
The sites display no evidence of human dwelling, and rarely encompass graves. This suggests that stone circles were constructed for ceremonies (perhaps religious ceremonies) and were in use on ceremonial occasions only. The type of ceremonies (if any) is entirely unknown. An alternative hypothesis is that they were a form of amulet or talisman, i.e., an entity acknowledging and appeasing supposed spirits dwelling in nature, meaning that their ceremonial use was secondary to their talismanic value, or equal to it.
The crudeness and 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. A stone circle is an entirely different entity from a henge, and different also from an isolated monolith, yet sometimes these other types of ancient stone monuments are found in close proximity.The earliest known circles were apparently erected around five thousand years ago during the Neolithic period and may have evolved from earlier burial mounds which often covered timber or stone mortuary houses.
The suggestion that they may have evolved from earlier burial mounds is undercut by the fact that, of the hundreds of Neolithic and Bronze Age circles that have been identified, none are provably centered on a burial. That suggests religious context, the details of which are still obscure
A "cromlech" is a monument of standing stones arranged in a circle, dated to the period of the European Neolithic known as the "Megalithic era".
More than 1,000 stone circles have been cataloged for Western Europe, mostly lying not more than 100 miles from the sea.
The arrangement of the stones may be in a circle, an ellipse, or more rarely a setting of four stones laid on an arc of a circle. The size and number of stones in a circle varies from example to example.