Proleek Dolmen lit up.

It is known as the ‘Giant’s Load’ and, when you stand under the great capstone of Proleek Dolmen, it’s not difficult to see why. This huge boulder is reputed to weigh around 40 tonnes, yet it sits comfortably on top of three upright stones as if it was a sheet of paper and not a giant rock.

Legend says the stone was carried there by a Scottish giant called Parrah Boug McShagean, who is reputed to be buried nearby. Another tale says it was brought by a giant from a nearby mountain. Proleek is one of Ireland’s best-known examples of what archaeologists call a Portal Tomb or Dolmen, and photographs of the monument are featured far and wide.

A new theory suggests the tomb may have been deliberately aligned towards Slieve Gullion, where on the summer solstice, the sun sets behind the mountain. Anthony Murphy, who is co-author of the book ‘Island of the Setting Sun - In Search of Ireland’s Ancient Astronomers’, says the opening of the portal tomb is roughly aligned towards summer sunset, which he observed directly a few weeks ago.

Proleek Dolmen frames the Summer Solstice sunset. Click for larger.

“This tomb seems to open towards Slieve Gullion, which is very interesting because Gullion has two passagetombs on its peak,” Mr Murphy said this week. “And this was a widespread practice in ancient times - to align one monument towards other monuments or significant landscape features in conjunction with astronomical events.” “The tomb is likely to have featured an alignment towards the moon also,” he said. “The moonset at the time of what astronomers call ‘major lunar standstill’ would probably set in line with the opening of the Proleek Dolmen.”

Mr Murphy and his coauthor, Louth artist Richard Moore, took these striking photos of the dolmen on Summer Solstice weekend 2008. “This is a technique called ‘painting with light’. We’ve done a lot of our photos like this, including the well-known night shot of Mellifont Abbey,” said Richard Moore. “It takes lots of practice, and plenty of time and patience, but the results are well worth it,” he added.