Gothic cathedrals date back many centuries, which has always made it difficult to prove one way or the other whether their structural steel components were ‘designed in’ or added during later maintenance and refurbishment.

That debate may now be at an end, as a team from CNRS in Paris claim to have developed a method of carbon-dating the ironwork in these cathedrals, proving once and for all that it was contemporary with the stone construction of the buildings.

Carbon dating requires organic material to be present – but as wood charcoal was used for smelting ore up to the Middle Ages, the tiny fragments of tree embedded into the iron allowed carbon-14 levels to be measured and, in turn, the age of the tree to be determined to within just a few years.

They found, for instance, that the structural steel supporting the world’s highest Gothic choir, at over 46 metres, dates to the known beginning of the construction around 1225 AD – and, therefore, was likely to have been included in the plans for the cathedral at Beauvais.

Meanwhile, at Bourges cathedral, an iron chain was found to be the same age as the building, but incorporated into it in an inconsistent way, passing around some columns and under others – suggesting it was an ad hoc solution added during construction, rather than in the initial design.