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and/or from the rocky beach at Clogherhead, County Louth, about 20 km to the north-east.
The facade and entrance was built with white quartz cobblestones from the Wicklow Mountains, about 50 km to the south; dark rounded granodiorite cobbles from the Mourne Mountains, about 50 km to the north; dark gabbro cobbles from the Cooley Mountains; and banded siltstone from the shore at Carlingford Lough. O’Kelly and his archaeological team, who believed that it would have taken a minimum of thirty years to build.
One of the most notable examples of art at Newgrange are the triskele-like features found on the entrance stone. It has been described as "one of the most famous stones in the entire repertory of megalithic art." Archaeologists believe that most of the carvings were produced prior to the stones' being erected, although the entrance stone was instead carved in situ before the kerbstones were placed alongside it.
It is approximately three metres long and 1.2 metres high (10 ft. Various archaeologists have speculated as to the meaning of the decoration, with some, such as George Coffey (in the 1890s), believing them to be purely decorative, whilst others, like M. O'Kelly (who led the 1962–1975 excavation at the site), believed them to have some sort of symbolic purpose, because some of the carvings had been in places that would not have been visible, such as at the bottom of the orthostatic slabs below ground level.
Many more artifacts were found in the passage in previous centuries by visiting antiquarians and tourists, although most of these were removed and missing or were held in private collections.
Nonetheless, these were sometimes recorded, and it is believed that the grave goods that came from Newgrange were typical of Neolithic Irish passage grave assemblages.
Extensive research on how the art relates to alignments and astronomy in the Boyne Valley complex was carried out by American-Irish researcher Martin Brennan.
The Newgrange monument primarily consists of a large mound, built of alternating layers of earth and stones, with grass growing on top and a reconstructed facade of flattish white quartz stones studded at intervals with large rounded cobbles covering part of the circumference.Various grave goods were deposited alongside the bodies inside the passage.Excavations that took place in the late 1960s and early 1970s revealed seven 'marbles', four pendants, two beads, a used flint flake, a bone chisel and fragments of bone pins and points.Several other passage tombs in Ireland are aligned with solstices and equinoxes, and Cairn G at Carrowkeel has a similar 'roofbox'. It is the most famous monument within the Neolithic Brú na Bóinne complex, alongside the similar passage tomb mounds of Knowth and Dowth, and as such is a part of the Brú na Bóinne UNESCO World Heritage Site.
After its initial use, Newgrange was sealed for several millennia.Twelve standing-stones survive out of a possible original thirty-five or thereabouts.