from inside by a heavy slab of stone, often fitted into grooves. The
niche on the right of the passage clearly served to hold a man, who
would command the passage itself and the staircase to the upper floor;
he would, moreover, be able to attack the undefended flank of an enemy
entering with his shield on his left arm. To the same effort at
impregnability we may safely ascribe the fact that the staircase leading
to the upper room did not begin on the floor-level of the passage, but
was reached through a hole high up in the wall. Many of the _nuraghi_
are surrounded by elaborate fortifications consisting of walls, towers,
and bastions, sometimes built at the same time as the dwelling itself,
sometimes added later. Those of Aiga, Losa, and s'Aspru are among the
most famous of this type. All the _nuraghi_ stand in commanding
situations overlooking large tracts of country, and the more important a
position is from the strategical point of view the stronger will be the
_nuraghe_ which defends it. All are situated close to streams and
springs of good water, and some, as for instance that of Abbameiga, are
actually built over a natural spring. At Nossiu is a building which can
only be described as a fortress. It consists of a rhomboidal enclosure
with _nuraghe_-like towers at its corners and four narrow gateways in
its walls. It is surrounded by the ruins of a village of stone huts.
There cannot be the least doubt that in time of danger the inhabitants
drove their cattle into the fortified enclosure, entered it themselves,
and then closed the gates.

Each _nuraghe_ formed the centre of a group of stone huts. Mackenzie has
described such a village at Serucci, where the circular plan of the
huts was still visible. The walls in one case stood high enough to
show, from the corbelling of their upper courses, that the huts were
roofed in the same fashion as the _nuraghi_ themselves. Another village,
that which surrounds the _nuraghe_ of Su Chiai, was protected by a wall