I’ve recently returned from holiday on the Glenelg peninsular in Scotland, just across from the Isle of Skye on the west coast. Three miles down the road were two brochs or dry stone, hollow walled towers that date from the 1st cent. BC/AD called Dun Telve and Dun Troddan.
Brochs are the most spectacular of a complex class of roundhouse buildings found throughout "Atlantic Scotland".
The construction is rather strange in that there are steps and floors in the hollow walls that suggest they served as corridors, although they do get rather narrow the further up you go.
Dun Troddan internal staircase
Brochs' close groupings and profusion in many areas may suggest that they had a primarily defensive or even offensive function, although it is probably best to consider broch sites individually in that there may never have been a single common purpose for which every broch was constructed.