From the top of Knowth’s great mound, my gaze leaps over its smaller satellite mounds and wanders across an expanse of summer-green fields. This is Brú na Bóinne, a vast neolithic complex looped by the River Boyne, where the landscape is dominated by three artificial “hills” that were layered over passage tombs built about 5,000 years ago.
The most famous of the three is to the south – Newgrange, which is aligned with the winter solstice sunrise. To the east is Dowth, which aligns with winter sunsets. And then there’s this one beneath my feet, the great mound, containing two back-to-back chambers facing east and west. As ever with such ancient structures, the big question is: what was it for?
The chambers could have been intended to catch the sunlight of the spring and autumn equinoxes (in March and September), when day and night are of equal duration. This is potentially affirmed by the equinoctial shadows cast by lone standing stones towards the east and west passage entrances. But Knowth was also a place of settlement and burial for thousands of years. All that human activity over the millennia damaged its passages, with the sunlight now only reaching a short distance along their lengths.
Another intriguing possibility is that the great mound is the result of neolithic people’s sophisticated knowledge of astronomy, which integrates an understanding of both the solar and lunar cycles. Knowth’s megalithic art – the largest collection in Europe – hints at this purpose. Much of the artwork is on the massive kerbstones that ring the great mound like a giant’s prayer beads. I head back down the slope and dawdle from stone to stone. The carved lines create abstract pictures that let the imagination soar. Concentric arcs could be the sun. Repeated waves might trace the moon’s path across the sky. And dazzling spirals remind me of Van Gogh’s Starry Night.
A series of rapid chitterings makes me look up. I’m close to the east entrance, where the reconstructed woodhenge (a circle of timber pillars) stands above the sockets of the original neolithic one. I think of those first builders. They too must have watched chittering swallows. They too must have seen how a flock carves the sky.
• Under the Changing Skies: The Best of the Guardian’s Country Diary, 2018-2024 is published by Guardian Faber; order at guardianbookshop.com and get a 15% discount
