The topography of the Queen City
  In 324, Constantine I (307-337) chose to fix his residence at Byzantium, an ancient Megarian colony, between the Black Sea and the Sea of Marmara (Propontis). The town was a naturaly fortified site surrounded by sea and provided with two harbours on the side of the Golden Horn. Constantine constructed a wall to its west, enlarged the already existing streets and hippodrome, multiplied the public places, which he adorned with statues and arches, and added a vast imperial palace and a few churches, such as the church of St Irene and that of the Holy Apostles.
  Constantinople's remarkable expansion in the decades following its inauguration (330) is witnessed by the increasing number of fora (open air plazas), monuments and mansions, its new harbour, and the double land walls (413) built under Theodosios II (408-450).
  Fifth century sources mention no less than 52 colonnades, 4 fora, 2 theatres in addition to the hippodrome, 322 streets, 5 imperial and 9 princely palaces, 4388 mansions, 8 public and 153 baths, 14 churches and 5 granaries, all within the inner Constantinian wall. The Mese was the city's main commercial street and a major artery for imperial processions and triumphs. It ran from the Milion, the first milestone of the empire, near St Sophia and the Hippodrome, to the Forum of Constantine, the Forum of Theodosios (Tauri), the Forum Amastrianum, the Forum Bovis and the Forum of Arkadios. Beyond that point, the Mese ran parallel to the shore until it reached the Golden Gate, the main gate of the Theodosian wall, used in imperial processions. Shortly after the Forum of Theodosios, at a cross-road known as the Philadelphion , the Mese forked, one arm extending in a northwesterly direction toward the Church of the Holy Apostles, the imperial mausoleum.
  From the Propontis to the Golden Horn, the city was protected by massive land fortifications, comprising an inner wall with towers, a lower outer wall, also with towers, and a moat. The sea front was protected by a single row of fortifications. Both the land and sea walls were built of bonded masonry, with alternating bands of brick and cut-stone facing, the latter enclosing a core of mortared rubble.
  The city soon competed in size, importance and splendor with the old metropolis' of Rome, Alexandria and Antioch. Like all great capitals, Constantinople was a melting-pot of peoples and languages, attracting provincials and barbarians alike, the former settling there or drifting in and out on business of all kinds, the latter as part of the servile class or of mercenary military units. By the sixth century, the city's population had grown to around 300000-400000.