A Night at the Broch   A broch  is an Iron Age drystone hollow-walled structure of a type found only in Scotland.  The word broch is derived from Lowland Scots 'brough', meaning (among other things) fort. In the mid-19th century Scottish antiquaries called brochs 'burgs', after Old Norse borg, with the same meaning.  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 Historical Monuments of Scotland (RCAHMS) identifies a total of 571 candidate broch sites throughout the country. The origin of brochs is a subject of continuing research. Sixty years ago most archaeologists believed that brochs, usually regarded as the 'castles' of Iron Age chieftains, were built by immigrants who had been pushed northward after being displaced first by the intrusions of Belgic tribes into what is now southeast England at the end of the second century BC and later by the Roman invasion of southern Britain beginning in AD 43. Yet there is now little doubt that the hollow-walled broch tower was purely an invention in what is now Scotland; even the kinds of pottery found inside them that most resembled south British styles were local hybrid forms. The distribution of brochs is centered on northern Scotland. Caithness, Sutherland and the Northern Isles have the densest concentrations, but there are also a great many examples in the west of Scotland and the Hebrides.  A few examples occur in the Borders (for example Edin's Hall Broch and Bow Castle Broch); on the west coast of Dumfries and Galloway; and near Stirling. In a c.1560 sketch there appears to be a broch by the river next to Annan Castle in Dumfries and Galloway. The original interpretation of brochs, favored by nineteenth century antiquarians, was that they were defensive structures, places of refuge for the community and their livestock.  Brochs' close groupings and profusion in many areas may indeed suggest that they had a primarily defensive or even offensive function. Some of them were sited beside precipitous cliffs and were protected by large ramparts, artificial or natural. Generally, brochs have a single entrance with bar-holes, door-checks and lintels. There are mural cells and there is a scarcement (ledge), perhaps for timber-framed lean-to dwellings lining the inner face of the wall. Also there is a spiral staircase winding upwards between the inner and outer wall and connecting the galleries. Brochs vary from 16–50 ft. in internal diameter, with 10 ft. thick walls. It is normal for there to be a cell breaking off from the passage beside the door; this is known as the guard cell.  It is generally accepted among archaeologists that brochs were roofed, perhaps with a conical timber framed roof covered with a locally sourced thatch.