Chalke: Principal Gate to the Sacred Palace
The City reconstructed: http://www.arkeo3d.com/byzantium1200/contents.html
With the creation of the Roman Empire, Byzantion continued as a modest city, with no substantial development discernible. At the end of the second century AD, however, after the death of Commodus, it backed the losing side in the civil war between Septimius Severus and Pescennius Niger. After a siege of two-and-a-half years (an indication of the strength of its position), it was starved into surrender. The walls were destroyed, and the city reduced to the status of a mere village in the territory of its neighbour, Perinthus. Its position, however, was still incomparable, and some revival, encouraged by Severus' son Caracalla, was inevitable, and the city was probably refortified. It played a role in the war between Maximinus and Licinius, and again between Licinius and Constantine. The importance of the site was clearly much greater than the small Greek city which occupied it. It could dominate not only the passage through the Bosporus to the Black Sea, but also one of the crucial crossings from Europe into Asia. It was adjacent to the still-wealthy provinces of Asia, while behind it were the rich and populous agricultural lands of the Balkans, which were now one of the primary areas for recruitment into the Roman armies, a fact demonstrated by the origin of the emperors themselves, including Constantine. Having gained the Empire, Constantine saw here the obvious place for the new Rome.
Thus the new city had as its raison d'etre the function of an Imperial capital, rather than as a city in the conventional, normal, Graeco-Roman manner. It was, like its Hellenistic forerunners, a dynastic city, and took its name (in Greek) from the emperor who founded it. It is now Constantinoupolis, Constantinople, Constantine's city, not Byzantion, and it owes nothing, other than its position, to its predecessor. From the outset it was intended for development on a grandiose scale, necessary if it was to be an effective alternative to Rome. An outer wall, running from the sea across the promontory to the Golden Horn, was placed some 4 km to the west of the old Greek city. Even this proved inadequate, and under Theodosius II the defensive fortifications were built 1.5 km further to the west, the area enclosed being extended from 6 to 14 km2. Even for Constantine's city, the population cannot have been found from the inhabitants of Byzantion. People must have been moved in on a colossal scale from other Greek communities in the area.
Functionally, however, the city did not depend on its population (for the size was largely a matter of prestige), or, strictly speaking, on its needs. Architecturally, the important element in the new plan was not a forum and its related public buildings, like traditional Rome or the lesser Graeco-Roman cities, but the palace, the building for the emperor, and the structures related to it. The antecedents for this, of course, go back to the palace buildings at Rome, and the palace buildings of Galerius, grafted onto the existing city of Thessalonike. At Constantinople the palace was placed over a substantial part of the old city, which was cleared for it, overlooking the sea, on the south-west of the hill which had carried the original city. The palace now had the role of an acropolis within the new, enlarged city. With it, as with the Palatine and other palaces, was immediately related the Great Hippodrome, which was not merely the locality for the chariot races, but also the place where the emperor made his appearances to the public. Thus the chariot races, and the factions that supported the different colours worn by the charioteers, usurped the place of the forum as the locality for the political interchange between the rulers and the ruled. Equally, and symbolic of the new order, the palace was also directly related to the Great Church, which was in an enclosure immediately to the north-east of the palace, on the ridge towards the former acropolis. This was the church dedicated to the Holy Wisdom (Hagia Sophia), a title which recalled Athena the goddess of wisdom and probably her role of poliouchos, protectress of the city, thus easing the acceptance of the new Christian forms by a population, many of whose members were probably of recent conversion.
Very little of early Constantinople survives, for a variety of reasons. Unlike Rome, Constantinople is quite prone to earthquakes, and these have periodically ruined or damaged its buildings. The turbulent history of the city, in its early days alone, was marked by riots and fits of incendiarism, quite apart from fires that broke out by accident. Earthquakes are recorded as having occurred, for example, in 407, 417 and 433, and there was a series of fires culminating in those started in the Nike riots (the watchword of the rioters), which led the Emperor Justinian to fear he had been deposed, in AD 526. In this riot, much of the palace area and the Great Church was destroyed and required total reconstruction, a dangerous consequence of the proximity of the Hippodrome to the palace buildings.
The damage caused by these incidents seems to have been exacerbated by another factor. When Constantinople was built, Constantine was in a hurry. Unlike Rome, the proper and established support for a massive building programme did not exist, and had to be developed. Moreover, Constantinople did not have available the pozzuolana that was responsible for the quality of Roman cement. Lime kilns had to be developed to provide the necessary mortar (their smoke in later times became such a nuisance that legislation had to be passed forbidding the presence of the kilns in the immediate vicinity of the city). Although lime mortar seems to have been adequate for the more limited building-programme of Galerius at Thessalonike, much of Constantine's building seems to have been rushed and gimcrack, and so particularly vulnerable to the effects of earthquakes. It was only after the passage of time that building methods suitable both to the resources, as well as the risks of the locality, were developed which made possible greater durability for the main structures, so that Justinian's replacement church of the Holy Wisdom had a dome made not from poured cement (as was the dome of Hadrian's Pantheon at Rome), but from mortared brickwork, and even that was damaged by a subsequent earthquake and reconstructed.