Stone upon stone, the towering embodiment of their builders’ wealth, status or hunger for defence, Scotland’s iron-age brochs have fascinated and confounded archaeologists for centuries.

The precise constitution of these architecturally complex roundhouses, and why they remain unique to Scotland, is the subject of ongoing research, but there is broad agreement that a broch is a drystone tower built between around 2,500 and 1,800 years ago, in the mid-iron age, often with cells and stairs built within the walls.

According to Historic Environment Scotland (HES), between 500 and 600 have been identified using this definition, scattered across the country but with the densest distribution in Orkney, Shetland, and Caithness.

On the Caithness coastline, north-east of Helmsdale, conservation work on the broch at Ousdale – now among the best preserved in the country and one of the few with evidence of a second floor – was weeks away from completion when it was abruptly halted by the lockdown.

With fresh gravel flooring ready to lay when restrictions allow, the Caithness Broch Project, which coordinated the £180,000 Ousdale preservation, will then be ready to proceed with its flagship experiment: building a new broch from the ground up for the first time in the modern age, with the aim of understanding through construction how these structures developed and what they signified to the people who built them.

“Experimental archaeology is a more practical and innovative way of dealing with the difficult questions posed by these enigmatic constructions,” explains Kenneth McElroy, the director of the Caithness Broch Project. “In turn, this helps us to better understand peoples of Scotland, and what drove them to build such impressive constructions.”

A handful of the most impressive brochs – Gurness, dominating the shoreline of Eynhallow Sound in Orkney, or the 13-metre Mousa broch in Shetland, which features in two Norse sagas – are open to the public. Many are cared for by HES or local authorities, but still more are lost beneath grassy tors, evidenced only by a few protruding stones.

Midhowe broch on the island of Rousay. Photograph: George Sargent/Reuters

Dr John Raven, the deputy head of casework at HES, suggests that a series of factors combined to create the context for the development of brochs. “In the background is a social crisis throughout north-western Europe in the mid-iron age which resulted the creation of hierarchies who sought to express their status and ownership by building complex structures. This was also a period of climate change which resulted in a significant expansion of peat growth in north and west Scotland, which limited the extent of good agricultural land and placed pressure on communities.

“It is also possible that communities were reacting to slave trading with communities to the south and later the knock-on effects of the expansion of Rome. The structural complexity of brochs also suggests the development of specialised building techniques which largely limited the spread to inter-connected communities.”

As well as a thrilling exercise in experimental archaeology, the construction of a new broch will preserve and promote the skills of drystone dyking, says McElroy. He is working with a firm of architects to identify a suitable site for the project before fundraising stars in earnest. Crucially, he adds, the newbuild broch could serve as a world-class tourist attraction to draw visitors to Caithness, an area often bypassed on the way to more familiar island destinations.

McElroy says: “There are so many unanswerable questions in archaeology, and in the past, but this should go some way to revealing more about our iron-age ancestors.”