But this is usually the form of all the Gallic walls. Straight
beams, connected lengthwise and two feet distant from each other at equal
intervals, are placed together on the ground; these are mortised on the inside,
and covered with plenty of earth. But the intervals which we have mentioned, are
closed up in front by large stones. These being thus laid and cemented together,
another row is added above, in such a manner, that the same interval may be
observed, and that the beams may not touch one another, but equal spaces
intervening, each row of beams is kept firmly in its place by a row of stones.
In this manner the whole wall is consolidated, until the regular height of the
wall be completed. This work, with respect to appearance and variety, is not
unsightly, owing to the alternate rows of beams and stones, which preserve their
order in right lines; and, besides, it possesses great advantages as regards
utility and the defense of cities; for the stone protects it from fire, and the
wood from the battering ram, since it [the wood] being mortised in the inside
with rows of beams, generally forty feet each in length, can neither be broken
through nor torn asunder.