The original complex of Newgrange was built between c. 3200 and 3100 BC. According to carbon-14 dates, it is approximately five hundred years older than the current form of Stonehenge and the Great Pyramid of Giza in Egypt, as well as predating the Mycenaean culture of ancient Greece. Some put its period of construction somewhat later, at 3000 to 2500 BC. Geological analysis indicates that the thousands of pebbles that make up the cairn, which together would have weighed about 200,000 tonnes, came from the nearby river terraces of the Boyne. There is a large pond in this area that is believed to be the site quarried for the pebbles by the builders of Newgrange. Most of the 547 slabs that make up the inner passage, chambers, and the outer kerbstones are greywacke. Some or all of them may have been brought from sites approximately 5 km away, from the rocky beach at Clogherhead, County Louth, about 20 km to the northeast. The facade and entrance were 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. The stones may have been transported to Newgrange by sea and up the River Boyne by fastening them to the underside of boats at low tide. None of the structural slabs were quarried, for they show signs of having been weathered naturally, so they must have been collected and then transported, largely uphill, to the Newgrange site. The granite basins found inside the chambers also came from the Mournes.