These bulwarks, renowned in antiquity for their strength, were faced with squared blocks of hard stone, bound together with metal clamps, and so closely fitted as to seem a wall of solid rock around the city. One tower was named the Tower of Hercules, on account of its superior size and strength, and seven towers were credited with the ability to echo the slightest sound made by the movements of an enemy, and thus secure the garrison against surprise. From the style of their construction, one would infer that these fortifications were built soon after Pausanias followed up his victory on the field of Platæa by the expulsion of the Persians from Byzantium. These splendid ramparts were torn down in 196 by Septimius Severus to punish the city for its loyalty to the cause of his rival, Pescennius Niger. In their ruin they presented a scene that made Herodianus[16] hesitate whether to wonder more at the skill of their constructors, or the strength of their destroyers. But the blunder of leaving unguarded the water-way, along which barbarous tribes could descend from the shores of the Euxine to ravage some of the fairest provinces of the Empire, was too glaring not to be speedily recognized and repaired. Even the ruthless destroyer of the city perceived his mistake, and ere long, at the solicitation of his son Caracalla, ordered the reconstruction of the strategic stronghold. It is with Byzantium as restored by Severus that we are specially concerned, for in that form the city was the immediate predecessor of Constantinople, and affected the character of the new capital to a considerable extent. According to Zosimus, the principal gate in the new walls of Severus stood at the extremity of a line of porticoes erected by that emperor for the embellishment of the city.[17] There Constantine subsequently placed the Forum known by his name, so that from the Forum one entered the porticoes in question, and passed beyond the limits of Byzantium.[18] Now, the site of the Forum of Constantine is one of the points in the topography of the capital of the Eastern Roman Empire concerning which there can be no difference of opinion. The porphyry column (Burnt Column) which surmounts the Second Hill was the principal ornament of that public place. Therefore the gate of Byzantium must have stood at a short distance from that column. According to the clearest statements on the subject, the gate was to the east of the column, the Forum standing immediately beyond the boundary of the old city.[19]