Feb. 24th, 2017
A typical broch stood from five to 13 metres high. It was a circular, two-storey, drystone, structure, accessed by a single door at ground level.
Inside was a main inner "chamber" from which smaller cells - either built into, or up against, the wall - branched off. A winding, stone staircase, housed within the broch's double walls, led upwards to elevated floors and finally the top of the structure.
Although, like the earlier roundhouses, it is possible that some brochs were no more than fortified dwellings, a widespread belief is that they had a defensive function and are characterised by immensely thick outer walls.
It is now believed, however, that, although defence may have played some part, they were more likely to have been built to impress - a monumental marker in the landscape, highlighting the owner's social status, wealth and power.
Orkney's brochs were feats of considerable architectural and engineering expertise, the key to which was the principle of double-skinned walls.
Stronger and more stable than a single wall, the brochs had two parallel walls built with a hollow space between. These two outer "skins" were bonded at certain heights by stone lintel slabs - a method that allowed the broch's constructors to build to greater heights than could be achieved with solid walls.
An intriguing element about the construction of Orkney's brochs, is that many of them were found to have an underground chamber, often accessed via a flight of stone steps.
At one time, these chambers were dismissed as domestic wells, or cellars, but recent research has hinted at a more ritual use.