How long till the equinox?

Brú na Bóinne: East entrance to Knowth passage tomb on the banks of the Boyne and part of the Newgrange World Heritage Site.

This is the entrance to the east facing passage of the main passage tomb; another passage faces west. Unlike the Newgrange tomb which is designed to be flooded with light on the Winter Solstice (21st December), Knowth is oriented to mark the Autumn and Spring Equinoxes. Before each entrance is a large standing stone (the one in the picture should be twice its current height but was broken at some point) which would cast its shadow into the passage at the appropriate time. The kerb-stone behind this stone has been etched with vertical lines suggesting it was placed as a solar calendar of sorts indicating by the shadow of the standing stone, when the equinox could be expected.

In the foreground is white quartz from Wicklow representing light or life while the darker stone is granite from the Mournes representing darkness or death; these interpretations are echoed in the Gaelic names for the two types of stone.

Knowth is the biggest of the 3 major passage tombs at Newgrange: Newgrange having the fancy frontage of Wicklow quartz and Dowth being the least of the 3. All of these tombs pre-date the pyramids at Giza by at least 500 years dating them as 5000 years old at around 3000BCE.

Knowth is the most interesting of the 3 sites if not the most impressive (Newgrange itself takes that title). The main tomb is the centre of a site containing another 18 or so lesser tombs. The main tomb is built upon a Mesolithic site with later Neolithic artefacts dated to 4,000BCE. Meanwhile, on top of the Neolithic structure is evidence of:

* a Celtic rath including a 5m deep trench dug into the neolithic tomb
* multiple early Christian settlements with several souterraines dug into the mound (causing the main east passage to collapse)
* a Norman tower house
* subsequent farming use up until 1962

The early Christian site - possibly a grange associated with the nearby Mellifont abbey - has several souterraines dug into the mound; these caused several of the standing stones in the main east passage to collapse making it currently impassable. The West passage is impassable too but by looters attempting to remove a large, carved stone basin which became wedged part-way down the passage. Evidently the tomb was built around the basin and its mate still in place in one of the chambers at the end of the east passage.

Set on a bend in the Boyne, the value of the site can be appreciated when standing on the top of the mound, surveying the surrounding country; even imagining when Ireland was clothed in oak forest, the view is exceptional in every direction and, of course, monitoring the river itself.

The guy who discovered the tomb had no idea what he had found: at that time the site was almost level with only a small rise in the centre. As the site was excavated the main mound was revealed as an elliptical tomb 80-95m in diameter and a maximum height of 15m along with companion small tombs and the remains of a wood-henge. At the end of East passage is a central area with 3 chambers; the corbelled roof creates a huge space 6m from floor to apex.

What distiguishes the Newgrange site and Knowth in particular is the extent of Neolithic art adorning the 127 kerb-stones around the mound and inside the passages. Over 2 thirds of all known such art is found here with the greater proportion located at Knowth.

The concrete bunker-like appearance of the entrance itself is to provide some structural stability to the tomb as it passes over the ditch and one of the souterraine descends close to the entrance. The holes in the earth just above the concrete lintel are house-martin nests; at present occupied with very noisy and presumably hungry fledglings.