The method of building employed in their erection, was generally that mentioned by Vitruvius, in whose time it originated, as 'opus reticulatum'.
The 'opus reticulatum' was composed of small bricks (or stones) set together on their angles, instead of horizontally, and giving the surface of a wall the appearance of a sort of solid network.

This was considered by some architects of antiquity a perishable mode of construction; and Vitruvius asserts that some buildings where he had seen it used, had fallen down.

From the imperfect specimens of it which remain in modern times, it would be difficult to decide upon its merits.

That it was assuredly insufficient to support the weight of the bank of the Pincian Mount, which rose immediately behind it, in the solitary spot described some pages back, is still made evident by the appearance of the wall at that part of the city, which remains in modern times bent out of the perpendicular, and cracked in some places almost from top to bottom.

This ruin is now known to the present race of Italians, under the expressive title of 'Il Muro Torto' or, The Crooked Wall.
We may here observe that it is extremely improbable that the existence of this natural breach in the fortifications of Rome was noticed, or if noticed, regarded with the slightest anxiety or attention by the majority of the careless and indolent inhabitants, at the period of the present romance.