A compartment in a tomb in which burials were placed. In court tombs and wedge tombs a chamber is a sub-division of the burial gallery. Portal tombs have single chambers and passage tombs can have anything from one to five chambers, although usually passage tombs are considered to have a main chamber with extra subsidary chambers.
Passage tombs are perhaps the most celebrated style of tombs, mainly due to the fantastic examples at Newgrange (County Meath), Knowth (County Meath) and Dowth (County Meath) in the Boyne Valley as well as those at Loughcrew (County Meath), which is by far the best place to experience these wonders.
The classical form of passage tomb is the cruciform style, where a long passage leads to a main chamber with 3 small chambers off, forming a cross when viewed from above. However, there are many other styles, some don't even have a passage! These other forms are with a round chamber (see Fourknocks (County Meath)), a polygonal chamber or in the form of a cross of Lorraine, which can be found at Seefin Hill (County Wicklow).
There is one form known as an undifferentiated passage tomb wherein the chamber is simply a broadening of the passage, such as at Matthewstown (County Waterford).
The passage and chamber was, once constructed, covered in a mound of earth or a stone cairn, which was in turn held in place with a kerb around its perimeter.
Perhaps what Irish passage tombs are most known for is the form of rock art more commonly called passage grave art, which can be seen in abundance along the Boyne Valley in the many cemeteries.