If we are to believe the Anonymus and Codinus, this was the circuit of Byzantium from the foundation of the city by Byzas to the time of Constantine the Great. On the latter point, however, these writers were certainly mistaken; for the circuit of Byzantium was much larger than the one just indicated, not only in the reign of that emperor, but as far back as the year 196 of our era, and even before that date.[[12]] The statements of the Anonymus and Codinus can therefore be correct only if they refer to the size of the city at a very early period.
One is, indeed, strongly tempted to reject the whole account of this wall as legendary, or as a conjecture based upon the idea that the Arch of Urbicius and the Arch of the Milion represented gates in an old line of bulwarks. But, on the other hand, it is more than probable that Byzantium was not as large, originally, as it became during its most flourishing days, and accordingly the two arches above mentioned may have marked the course of the first walls built beyond the bounds of the Acropolis.
We pass next to the third line of walls which guarded the city, the walls which made Byzantium one of the great fortresses of the ancient world. These fortifications described a circuit of thirty-five stadia,[[13]] which would bring within the compass of the city most of the territory occupied by the first two hills of the promontory. Along the Golden Horn, the line of the walls extended from the head of the promontory to the western side of the bay that fronts the valley between the Second and Third Hills, the valley of the Grand Bazaar. Three ports, more or less artificial,[[14]] were found in that bay for the accommodation of the shipping that frequented the busy mart of commerce, one of them being, unquestionably, at the Neorion.[[15]]
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]]
The language of Zosimus, taken alone, suggests, indeed, the idea that the gate of Byzantium had occupied a site to the west of the Forum; in other words, that the Forum was constructed to the east of the gate, within the line of the wall of Severus. For, according to the historian, one entered the porticoes of Severus and left the old town, after passing through the arches (δι᾽ ὧν) which stood, respectively, at the eastern and western extremities of the Forum of Constantine. This was possible, however, only if these various structures, in proceeding from east to west, came in the following order: Forum of Constantine; porticoes of Severus; gate of Byzantium. On this view, the statement that the Forum was “at the place where the gate had stood” would be held to imply that the porticoes between the Forum and the gate were too short to be taken into account in a general indication of the Forum’s position. But to interpret Zosimus thus puts him in contradiction, first, with Theophanes, as cited above; secondly, with Hesychius Milesius,[[20]] who says that the wall of Byzantium did not go beyond the Forum of Constantine (οὐκ ἔξω τῆς ἐπωνύμου ἀγορᾶς τοῦ βασιλέως); thirdly, though that is of less moment, with the Anonymus[[21]] and Codinus,[[22]] who explain the circular shape of the Forum as derived from the shape of Constantine’s tent when he besieged the city.
Lethaby and Swainson[[23]] place the Forum between the porticoes of Severus on the east and the gate of Byzantium on the west, putting the western arch of the Forum on the site of the latter. They understand the statement of Zosimus to mean that a person in the Forum could either enter the porticoes or leave the old town according as he proceeded eastwards or westwards.
From that gate the wall descended the northern slope of the hill to the Neorion, and thence went eastwards to the head of the promontory.[[24]] In descending to the Golden Horn the wall kept, probably, to the eastern bank of the valley of the Grand Bazaar, to secure a natural escarpment which would render assault more difficult.
Upon the side towards the Sea of Marmora the wall proceeded from the main gate of the city to the point occupied by the temple of Aphrodite, and to the shore facing Chrysopolis.[[25]] The temple of the Goddess of Beauty was one of the oldest sanctuaries in Byzantium,[[26]] and did not entirely disappear until the reign of Theodosius the Great, by whom it was converted into a carriage-house for the Prætorian Prefect.[[27]] It was, consequently, a landmark that would long be remembered. Malalas[[28]] places it within the ancient Acropolis of the city. Other authorities likewise put it there, adding that it stood higher up the hill of the Acropolis than the neighbouring temple of Poseidon,[[29]] where it overlooked one of the theatres built against the Marmora side of the citadel,[[30]] and faced Chrysopolis.[[31]] From these indications it is clear that the temple lay to the north-east of the site of St. Sophia, and therefore not far from the site of St. Irene on the Seraglio plateau.