(A simple passage grave in Carrowmore near Sligo in Ireland, https://en.wikipedia.org/wiki/File:Thap_passage_tomb.JPG)
A passage grave is a generally a tomb from Neolithic. Some contain only one single room, while others may have sub-rooms accessible from the main burial chamber. The latter constructions are often arranged in a cross shape, being called cruciform passage grave. Passage graves, particularly the most recent, sometimes are surmounted by a cairn.
The cairn type of passage graves often have elaborated corbelled ceilings instead of simple slabs. In some sites, prehistoric art is present with engraved stones. In a number of outstanding examples, the hall itself is positioned so that the sun’s rays penetrate to a particular time of year, for example at sunrise at the winter solstice, or sunset at the time of the equinox.
In the 1960s, Irish archaeologists Sean O’Nuallain and Ruaidhri De Valera distinguished four categories of megalithic tombs: passage graves, passage cairns, dolmens and wedge tombs. But only the firsts seems to have been widely used throughout Europe.
The passage graves abundantly meet the entire Atlantic coast of Europe. They are found in Ireland, Great Britain, France, Scandinavia, northern Germany, in the province of Drenthe in the Netherlands, and in the Iberian Peninsula in parts of the Mediterranean and along the northern coast of Africa. The oldest passage graves appear to have had the form of small dolmens or small stone buildings. In Ireland and Great Britain, the passage graves are often assembled in large groups, known as “cemeteries” by some. Many recent passage graves were built on heights, indicating that their builders wanted them to be seen at a great distance.