The Megalithic phenomenon started in western central Portugal about 4800 BC. It spread north into Brittany and thence to the UK and south and west into Extremadura and Andalucia.
Megaliths, literally 'large stones', usually refer to standing stones (often called menhirs), stone circles, tombs or dolmens, tholoi (a dome-shaped tomb built from bricks or shaped stones, usually with a capstone sometimes called a false dome tomb), and hypogea (a tomb excavated underground).
The first megaliths were built in Andalucia in the westernmost province, Huelva, from about 3400 BC (Casullo). The practice extended over the next few hundred years, via the valley of the Rio Guadalquivir and the passes between the mountain chains that run west to east, through to the easternmost reaches of Andalucia and beyond.
Menhirs and stone circles, whilst common in Portugal, are rare in Andalucia, mainly confined to the western part of the region although some menhirs were erected and then reused later in dolmens a little further east. It appears that menhirs and stone circles were already largely redundant by the time of the first megaliths in Andalucia.
This series concentrates on the dolmens of Andalucia. Some, such as the Dolmen de Soto and the dolmens of Antequera were huge affairs that required the work of hundreds of individuals. The vast majority are much smaller, such as those along the Rio Gor in Granada province, even these would have needed a dozen or so strong men to maneauvre the large stones.