Although megaliths (standing stones) can be found in other places in Portugal, in the eastern part, called the Alentejo, there are many of them. I spent a day "hunting" them in the general area of the town of Évora. They are mostly off the main roads along gravel and dirt roads. It was fun.
Menhir or menir - single standing stone.
Cromeleque or cromlech - group of standing stones
Dolmen - four or more large standing stones, with an enormous stone slab on top, providing some kind of a roof.
Neolithic period is a period along the human technology development line, from ± 10,000 to 4,000 BC, when the Bronze period started. The Neolithic period follows the Stone age and is a lot about the development of farming.
A lot of theories surround the megaliths. People like to be dramatic and will easily think of burial grounds, great religious actions and the like. Fact is that nobody knows for sure. For instance dolmen are thought to be a group burial tomb, but human bones were uncovered in only 1% of them. So, whatever your theory, don't fall in love with it.
Bottom left - Cromeleque dos Almendres (Almendres is a tiny village)
Top left - Menir da Bulhoa. Look closely halfway up and a bit to the right; see the snake-like relief, as if made by three fingers drawing in mud
Top, second from left - Menir dos Almendres (2.5 kms from the cromeleque). If you drew a line on a map, from the middle of the cromeleque to this menir, it describes the exact path of the sun on equinox days.
Top, second from right - Menir do Outeiro (another tiny village)
Top right - one of the menhirs in the cromeleque dos Almendres. The scribbles on this one is the best visible
Bottom right - Anta-capela de Nossa Senhora do Livamento. This chapel was originally a dolmen. Spaces between vertical stones filled in to form walls and a quaint cupola on top of the roof slab.
Middle - another carving on one of the cromeleque dos Almendres stones.
Bottom, middle - maybe megaliths have something to do with fertility. I took this picture in one of their calmer moments, at cromeleque dos Almendres.