sea-coast were often so placed as to communicate with each other for
long distances up the valleys, by signal by day, and beacon fire at
night, and so far as they are traceable, the positions of most of them
in Sutherland and Caithness are indicated on the map by circles.

Built invariably solely of stone and without mortar, in form the
brochs were circular, and have been described as truncated cones
with the apex cut off,[7] and their general plan and elevation were
everywhere almost uniform. The ground floor was solid masonry, but
contained small chambers in its thickness of about 15 feet. Above the
ground floor the broch consisted of two concentric walls about three
feet apart, the whole rising to a height in the larger towers of 45
feet or more, with slabs of stone laid horizontally across the gap
between and within the two walls, at intervals of, say, five or six
feet up to the top, and thus forming a series of galleries inside
the concentric walls, in which large numbers of human beings could be
temporarily sheltered and supplies in great quantities could be stored
for a siege. These galleries were approached from within the broch by
a staircase which rose from the court and passed round between the two
concentric walls above the ground floor, till it reached their highest
point, and probably ended immediately above the only entrance, the
outside of which was thus peculiarly exposed to missiles from the end
of the staircase at the top of the broch. The only aperture in the
outer wall was the entrance from the outside, about 5 feet high by 3
feet wide, fitted with a stone door, and protected by guard-chambers
immediately within it, and it afforded the sole means of ingress to
and egress from the interior court, for man and beast and goods and
chattels alike. The circular court, which was formed inside, varied
from 20 to 36 feet in diameter, and was not roofed over; and the
galleries and stairs were lighted only by slits, all looking into the