There are many other monuments on the ridge of Newgrange besides the great mound itself, and indeed many more were found on the floodplain below the passage graves over the summer of 2018 due to the unusually dry conditions.
During Professor Michael O'Kelly's exacvation of the stone circle, a series of pits were discovered nine meters out from the kerbstones of Newgrange and running beneath the circle of standing stones, indicating that the pits were older.
O'Kelly got C14 dates from samples taken from several pits, all of which were dated to the Bronze age. More interested in the Neolithic aspects of the Newgrange monument, O'Kelly had little to say about the pits in his book on Newgrange, which was published in 1982.
Also in 1982, archaeologist David Sweetman was charged with excavating a site for the location of a new guide hut. As Sweetman was digging in the south east portion of the Newgrange compound, close to the standing stone known as the Dowth pillar, he discovered an arc of pits similar to those discovered by O'Kelly twenty years earlier. Sweetman suspected they were part of the same monument and three test trenches proved that this was indeed the case.
Around the same time a second smaller circle of pits was found on the northwest side of Newgrange. This second circle is about the same size as the restored example at Knowth, one kilometer to the west.
The Bronze Age
The Newgrange woodhenge is approximately 100 meters in diameter, about the same size as the massive circle of standing stones surrounding Newgrange. Six rows of pits and post holes probably held timber uprights, which may well have been lintelled like the famous examples at Stonehenge.
Henge such as the Newgrange woodhenge are generally dated to the transition period between the neolithic and the bronze ages: younger than the huge mound but older than the stone circle. Charred bones of many animals but largely pig were found by Sweetman in many of the holes. The neolithic monument Site Z is within the circle, and possibly another site, Z1. About 100 meters to the east is the terminal of the Newgrange cursus, a ceremonial causeway or walkway that has not yet been dated.
There are four henges in the Boyne Valley dating to the late neolithic. One of the largest henges in the country, Site Q, is one kilometer east of Dowth. They are thought to belong to a time when many people were coming to visit the Boyne Valley: possibly neolithic pilgrims visiting in much the same way as happens at holy sites and shrines today.
The timber henge may have an astronomical purpose. A viewer standing on Site B on the flood plain below could watch midsummer sunsets and midwinter moonsets dropping between Sites K and L, Newgrange, and extreme moonsets through the timbers of the henge. A concern for studying the movements of the heavenly bodies in this region of the sky is found at Carrowkeel in County Sligo, in the chamber of Cairn G in particular.