When radiocarbon dating was first developed in the late 1940s by the American scientist, Willard Libby, these assumptions seemed to be confirmed. Twenty years later, however, when the technique was refined by reference to tree-rings, the archaeological world was shocked. Many of these monuments were shown to be much older than had previously been thought. Analysis of charcoal from the passage grave of Kercado, in Brittany, suggested that it had been built between 5200 and 4360 BC, at least 3000 years earlier than the Treasury of Atreus.
The Kercado date is now recognised as a very imprecise one, and the most recent research suggests that the earliest European passage graves were built in the late 5th, rather than the 6th Millennium BC, but this, nonetheless, rules out any possibility that they were inspired by any prototypes in the Mediterranean world.
A further shock came in 1983, when my late friend and colleague, Professor Jean L'Helgouac'h, published a paper in which he demonstrated that several of these passage graves incorporated the shattered remnants of a yet earlier phase of megalithic activity. At Locmariaquer, on the western shores of the Golfe du Morbihan, there had once been an alignment of standing stones carved with symbols, including images of stone axes. One of these is still standing, but has been incorporated as the back-stone of the passage grave of La Table des Marchand.
Another, the largest of all stones ever raised by prehistoric people anywhere in the world, lies broken in four pieces nearby. This was originally more than 20 metres high, with a weight of 280 tonnes. It seems to have been raised around 4700 BC, and to have fallen around seven hundred years later, probably as the result of an earthquake.
Another stone, carved with images of a hafted axe, a bull, a goat and an enigmatic symbol, was broken into three pieces, each of which has been incorporated in a different monument (La Table des Marchand, Gavrinis and Er Grah). Yet another is incorporated as a capstone of the nearby passage grave of Mane-Rutual.
These stones were erected by some of the earliest farmers in Europe, and the symbolism of the one shown above seems to encapsulate the new agricultural way of life. Whilst the largest of the stones may have been felled by an earthquake, the others seem to have been deliberately smashed and reused. Was the earthquake itself seen as a portentous omen, prompting the first of many waves of iconoclasm in Europe?
This iconoclasm, however, was not limited to the south of Brittany. As L'Helgouac'h and his colleague, Serge Cassen, showed me around their excavations at Locmariaquer in the late summer of 1988, and as we later shared a bottle of Muscadet, I realised not only that the first European megaliths must have been built more than five centuries earlier than any of my tutors at Cambridge had dared to imagine, but also that I knew of other examples of shattered idols incorporated in later passage graves: the "cup-marks" of La Hougue Bie on Jersey (a site that I would go on to excavate myself, with the help of L'Helgouac'h's students, as well as my own), and the so-called "Guardian" of Le Dehus on Guernsey.
What I did not know, however, on that most memorable of days, was that I would go on to write novels in which the builders of these monuments would feature as characters: novels which, sadly, my friend, Jean L'Helgouac'h, would not live long enough to read.
Mark Patton's novels, Undreamed Shores, An Accidental King and Omphalos, are published by Crooked Cat Publications, and can be purchased from Amazon.