The Roman general began by attempting to repeat the device of his predecessor, attacking the defences in the same place and by the same means; but, just as his mine was completed, the new wall with its framework of wood sank quietly into the excavation, without suffering any disturbance of its parts, while enough of it still remained above the surface to offer an effectual bar to the assailants.
It seemed hopeless to recommence the mine in this place, and elsewhere the nature of the ground made mining impossible; some other mode of attack had therefore to be adopted, or the siege must have been abandoned.

Rome generally took towns by the battering-ram; but the engines in use were of such heavy construction that they could not be dragged up an ascent like that upon which Petra stood.

Bessas was in extreme perplexity, when some Hunnic allies, who happened to be in his camp, suggested a mode of constructing a ram, as effective as the ordinary one, which should nevertheless be so light that it could be carried on the shoulders of forty men.

Three such machines were quickly made; and under their blows the wall would soon have given way, had not the defenders employed against them the terrible agency of fire, showering upon them from the walls lighted casks of sulphur, bitumen, and naphtha, which last was known to the Greeks of Colchis as "Medea's oil." Uncertain of succeeding in this attack, the Roman general gallantly led a scaling party to another portion of the walls, and, mounting at the head of his men, attempted to make good his footing on the battlements.

Thrown headlong to the ground, but undeterred by his fall, he was about to repeat his attempt, when he found it needless.
Almost simultaneously his troops had in two other places penetrated into the town.