The construction of these structures dates back to the 6th millennium BC. They were rediscovered in 1966 by Henrique Leonor Pina, who was carrying out field work relating to the country's geological charts. The excavation of the site unearthed a series of both megalithic and neolithic construction phases; Almendres I 6000 BC, Almendres II 5000 BC, and Almendres III 4000 BC. The relative chronology of the cromlech and menhirs is extremely complex and covers a period from the Neolithic to Chalcolithic. It is believed that the monument either had a religious/ceremonial purpose or functioned as a primitive astronomical observatory.
Architecture
Located off the national roadway from Évora to Montemor-o-Novo, in the former-civil parish of Nossa Senhora de Guadalupe, the cromlech is situated just after the village of Guadalupe, in Herdade dos Almendres. It is located in the southwest of the property, while the menhir is situated on the eastern limits of the estate facing the sunrise over the Serra de Monfurado, isolated from the local community. A pedestrian trail was defined by the localmunicipal council, and integrated into the municipality's "megalithic route" that follows the prehistoric remnants through the region. The complex, organized in a circular pattern, is marked by a forest of about 95 granite monoliths, deposited in small groups. The older monoliths are formed as two or three concentric circles of smaller monoliths in the western part of the complex, while the Middle Neolithic structures consist of two ellipses and large menhirs. In the Late Neolithic phase the earlier constructions suffered modifications, transforming it into a site for social or religious rituals. Ninety-two of the menhirs form two grounds, which were built and oriented to different directions associated with the Equinox. Many of the stones were unearthed where they stood/fell, and were rebuilt/erected by Mario Varela Gomes, based on criteria established from research and rediscovery of the original bases. The complex's latitudinal position is about the same as the maximum moon elongation ; comparably, another latitude where this occurs is associated with Stonehenge. Although there are many large solitary 2.5 to 3.5 metres rounded/elliptical stones, most are smaller and formed into groups. The cromlech occupies an area of 70 by 40 metres, oriented along an axial alignment northwest to southeast. The columns show signs of profound erosion, especially in those surfaces exposed to the elements, although decoration is still visible. These designs take the form of lines and radials, at least two on each stone. About a dozen monoliths exhibit some form of carved drawings, of which four exhibit only small circular holes. Monolith number 8, with a cut flat top at about breast level and showing several dimples, might have served for finer astronomical observation, specially spring equinox observation, by putting small stones on the dimples. These observations might also be made from stone 39, on the eastern focal point of the elliptic layout. Menhir 48, also exhibits a schematized anthropomorphic representation, surrounded by circles and associated with a crozier. An isolated single menhir, approximately 4.5 metres tall and 0.9 metres in diameter is located near the residences, or 1400 metres northeast of the main complex. A line from the Almendres Cromlech to this menhir points roughly towards the sunrise in the Winter solstice.
