Brochs are often referred to as ‘duns’ in the west. Antiquaries began to use the spelling ‘broch’ in the 1870s.
A precise definition for the word has proved elusive. Brochs are the most spectacular of a complex class of roundhouse buildings found throughout “Atlantic Scotland”. The Shetland Amenity Trust lists about 120 sites in Shetland as candidate brochs, while The Royal Commission on the Ancient and Historic Monuments of Scotland identifies a total of 571 candidate broch sites throughout the country.
Researcher Euan MacKie has proposed a much smaller total for Scotland of 104.
The origin of brochs is a subject of continuing research. Sixty years ago most archaeologists believed that brochs, usually regarded as castles, were built by immigrants who had been displaced and pushed northward, first by the intrusions of Belgic tribes into what is now south-east England towards the end of the second century BC and later by the Roman invasion of southern Britain from AD 43 onwards.
Yet there is now little doubt that the hollow-walled broch tower was purely an invention from what is now Scotland, or that even the kinds of pottery found inside them that most resembled south British styles were local hybrid forms. The first of the modern review articles on the subject (MacKie 1965) did not, as is commonly believed, propose that brochs were built by immigrants, but rather that a hybrid culture of a small number of immigrants with the native population of the Hebrides produced them in the first century BC, basing them on earlier, simpler promontory forts.