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The Gauls constructed their walls in this manner: beams were placed
horizontally on the ground, in a direction perpendicular to the line of
the enclosure,[477] at intervals of two feet from each other; they were
bound together on the side of the town; by cross-beams, usually of forty
feet in length, firmly fixed in the ground, and the whole covered with a
great quantity of earth, except on the           side, where the
intervals were furnished with large blocks of rock, and formed a facing.