Newgrange is what is known as a Megalithic burial chamber.  The megalithic tombs are built usually of large stones, and they vary considerably in size and shape. The simplest form is the dolmen with between three and seven legs supporting one or two capstones.

A more complicated form of megalithic tomb is represented by what is known as a court-cairn or court-tomb. This has the form of a rectangular burial chamber, often divided up by jambs and sills, and entered from a court or forecourt which is roughly semi-circular in shape and in which some form of funerary ritual probably took place.

It was around 2500BC, or possibly somewhat earlier, that art was first applied to architecture in Ireland, when the two combine on what are known as passage graves or passage tombs. These passage graves are also megalithic tombs, but they differ considerably in shape from dolmens and court-cairns. They consist of one or two tomb-chambers roughly in the centre of a large round mound of earth or stone, which as the name implies are reached by means of a passage from the edge of the mound.

The most famous of all Irish passage graves is Newgrange, which, with its close companions Knowth and Dowth, forms a cemetery group in a bend of the river Boyne some kilometres upstream from Drogheda.

The great mound at Newgrange is about 11m. (36ft) high and about 85m. (280ft) in diameter, a size so impressive that it presupposes a well-organised society capable of building it. The passage, lined and roofed with large stones, slopes gently upwards over a distance of 18.9m. (62ft) before it opens into the burial chamber, off which there are three tomb-niches with stone basins. The roof of the chamber is of corbel construction and rises to a lofty height of about 6m. (20ft). The corbel technique required layers of flat stones to be laid roughly in a circle, each layer jutting inwards beyond the one below it until the circle was sufficiently small to be closed by a single stone at the top. The stones used in this way at Newgrange tilt downwards away from the tomb – a measure designed to ensure that any water which percolated through from the top of the mound would not penetrate into the chamber. Another ingenious method employed apparently for the same purpose was the sinking of small continuous grooves in the upper surfaces of the roof-stones of both chamber and passage to serve as channels to drain off surplus rainwater. The dryness of the tomb to this day is indeed a great compliment to the ingenuity of its builders.

The burial mound at Newgrange stands off-centre in a circle of large standing stones of which 12 still survive out of the 35-38 which must originally have made up the full circle. This circle may have been in existence before the tomb was built, and could have served for the recording of astronomical observations used in the planning of the tomb. It is certainly remarkable that if the line from the centre of the tomb-chamber to the centre of the entrance of the passage is extended to the horizon, it marks the point where anyone standing at the tomb could see the sun rising on 21 December,the shortest day of the year. That this is not just coincidence is demonstrated by the fact that above the entrance to the passage there is a small cavity known as the ‘roof box’, the sole purpose of which appears to have been to allow the sun to shine through a gap in the roof-stones of the sloping passage at a sufficiently high level for its rays to reach the central point of the tomb on and around the shortest day of the year.

The civilisation of the builders and designers of this tomb must have been sufficiently far advanced for them to have possessed an annual calendar, on which the orientation of the tomb and its passage must have been based. This need not surprise us greatly, if we remember that at the time when Newgrange was built the civilisation which constructed the pyramids in Egypt had already long possessed such a calendar.

But what distinguishes the passage graves above all from the other kinds of megalithic tombs in Ireland is the fact that dome of them, particularly those in the eastern half of the country, bear ornamentation on some of their stones. This consists in the main of purely geometric motifs, such as circles, spirals, arcs, zigzags, lozenges or diamonds, dots in circles and wavy, parallel or radial lines.

Newgrange is not the only decorated tomb of its type in Co. Meath. The neighbouring tumuli of Knowth and Dowth also bear somewhat similar decoration.

Of all the Irish passage graves, perhaps the most unusual is that at Knowth, which recent excavations have shown to have not one but two burial chambers placed practically back to back.

One stone in the passage of one of the chambers at Knowth is almost certainly a stylisation of the human race. Passage-grave art is normally considered to be non-representational and geometrical. One stone in the chamber at Newgrange would seem to represent a fern.

Stone balls and small beads in the shape of miniature hammers have been found in the graves. Much of the pottery is of poor fabric, its surface pierced by a series of jabs, though some Late Stone Age pottery has beautiful grooved decoration.