The Brownshill dolmen is a pretty spectacular example due to its massive capstone. It is classified as a portal tomb. These tombs usually consist of two large portal-stones which define an entrance and a back-stone, all of which support the capstone. The capstone on this Dolmen is believed to be one of the largest and heaviest in Europe weighing in at around 150 tons.
The word Dolmen aparently comes from the Breton language, Dol table and Men stone.
This structure was built by Irelands first farmers sometime between 4000 and 3000 BC, during The Neolithic period, or New Stone Age, which is characterized by the beginning of a settled human lifestyle. People learned to cultivate plants and domesticate animals for food, rather than rely solely on hunting and gathering.
This site remains unexcavated and was probably buried under a mound of earth as is the case with most of these kinds of neolithic sites.