Iron working has been found throughout Shetland, including Unst. This was a time of considerable change in Shetland. There must have been a threat from invaders for this was the era of the Broch building.
A series of these huge structures were built in strategic sites, mostly along the shores, always in sight of another and their remains can still be seen, in spite of often being robbed of good building material. They were built to a common standard and Unst probably boasted ten of them.