1. Byzantion

Although there is evidence of settlement from as early as the late third millennium B.C., the earliest substantial habitation of the area occurred in the 7^th c. B.C. with the foundation of the city of Byzantion,¹ a colony of the Greek city of Megara. The name derives from its legendary founder, Byzas, the son of the nymph Semestre or of Poseidon and Keroessa, daughter of Io.² There is mention of another founder by the name of Antes and it appears that the two names were combined to form the city’s toponym.

The city came to the forefront in the 2^nd century AD, when it opposed the Roman emperor Septimius Severus in the civil war. Severus razed it to the ground and then rebuilt it, renaming it Augusta Antonina in honor of his son.

Archaeological evidence from Byzantion is scarce. Several of its ancient structures were incorporated into the new city and survived well into the Byzantine period.³Severus destroyed the ancient wall, passing shortly to the east of what was to become the Forum of Constantine, but it was rebuilt later in the 3^rd century.⁴ The cemetery of the city was located outside the walls.⁵ The acropolis (on the Seraglio point) had three temples, dedicated to Aphrodite, Artemis, and the Sun God. Another temple dedicated to Poseidon is also mentioned in the sources. There were at least two ports inside the walls, the Bosphorion or Prosphorion on the 5^thregion and the Neorion on the 6^th, with an agora next to it, later to become the Strategion. Other monuments included another agora called Tetrastoon (later to become the Augustaion, to the south of Hagia Sophia), the theater to the east of the acropolis, the amphitheater or Kynegion in the region of Mangana, situated to the east of the acropolis, and two baths (the baths of Achilles with a gymnasium nearby, and of Zeuxippos), the Hippodrome, and the aqueduct of Valens, actually built by Hadrian. The population of Byzantion is estimated between 20,000 and 50,000 inhabitants.

2. The selection of the site

The creation of imperial residences was a usual practice of the Tetrarchy. Such examples included, among others, Milan, Nicomedia, and Thessalonike. The foundation or re-foundation of a city as an imperial residence was followed by a more or less extensive reconstruction program aimed at beautifying the city particularly with large buildings, such as a hippodrome, imperial mausolea, and a palace. Constantine selected the rather insignificant site of Byzantion apparently because he appreciated its strategic advantages.⁶ It controlled the narrow channel that connected the Black Sea and the Mediterranean; it laid in the intersection of major highways, including the Via Egnatia, going both east and west; it was close to the thriving coastal cities of Asia Minor; and it provided quick access to the two most troublesome borders of the empire at the time, the Danube frontier and the boundary with Persia. The site had two major disadvantages: there was no natural defensive barrier to the west of the city (addressed with the erection of the land walls); and there were not any natural sources of water (which was remedied by the construction of an elaborate aqueduct system).Constantine founded the city in 324 and dedicated it on 11 May 330. Its name, Constantinopolis Nova Roma (Constantinople, the New Rome) signified Constantine’s intentions of recreating in the Bosphoros the glory of old Rome.⁷

3. The walls and the Forum of Constantine

Constantine’s architects and engineers embarked on a significant building project. Of prime importance was a construction of a wall, which was located approximately 3 km to the west of the walls of Byzantion. Although nothing survives today, parts of the Constantinian wall (such as its Golden Gate or Gate of Satourninos) were preserved in the medieval city and even after the Ottoman conquest. Just outside the ancient walls a large circular forum (known as the Forum Constantini) was built.⁸ At the center there was a porphyry column, which still survives today under the name of Çemberlitaş, surmounted by a colossal statue of Constantine as Helios. The building of the Senate was located in the north side of the forum. Its portico housed the statues of Athena and Thetis. Across from the Senate there might have been a nympheum.

4. The Great Palace and adjacent buildings

The earliest phase of the palace, constructed by Constantine and his immediate successors, was located to the southeast of the city, between the Hippodrome and the sea, an area occupied today by Sultanahmed (the Blue Mosque).⁹ It included residential quarters (Daphne), the quarters of the imperial guards, the Tribunal or Delphax, the Augusteus, probably a throne room, and an audience hall called Consistorium. A second Senate building and the Basilica were located close to the palace. Close to the Basilica the Milion, probably a tetrapyle, marked the beginnings of the city’s main avenue.¹⁰

The Hippodrome, a sports ring dedicated to chariot races and the center of the city’s public life, was adjacent to the palace.¹¹ According to the legend, the construction of the hippodrome begun under Septimius Severus and was completed by Constantine. The emperor attended the games and other functions from the Kathisma, an imperial box connected directly with the palace through a spiral staircase. Parts of Constantinople’s hippodrome still survive today.

The baths of Zeuxippos, reputedly built by Severus and enlarged by Constantine, were located in the northeast corner of the hippodrome. The baths were famous for the collection of antique statuary that decorated them.

5. Streets

The main artery was called Mese (lit. "middle street"), it was porticoed, and crossed the city from East to West. The Mese bifurcated ca. 1 km west of the Forum Constantini, with one branch leading southwest to the Golden Gate, and the other continuing to the northwest. The place were the Mese split was called Philadelphion (close to where Laleli camii is located today), decorated with a porphyry column, and statues of Constantine’s family members.¹² The Capitolium was located nearby. It appears that Constantinople inherited from Byzantion a relatively regular street layout which was later expanded.¹³

6. Churches and sanctuaries

Constantine's attitude towards pagan culture and sanctuaries was somewhat ambivalent. He certainly did not strive to make his new capital a Christian city as opposed to its pagan past as Byzantion, although the pagan aspect of the city was largely reduced in his days. Rather he incorporated the main elements of Byzantion's paganism to his imperial ideology, according to a long-standing Roman tradition. Thus, he made two pagan sanctuaries flanking a portico of the Tetrastoon, one of Rhea/Kybele and one of Tyche of Rome, which were most probably minor architectural formations and not actual sanctuaries; these two divinities were associated with the Tyche of Constantinople.¹⁴ He also systematically transported ancient sculpture to Constantinople, a practice that later emperors continued.¹⁵ Although he may have converted some pagan temples into Christian churches, such as the martyrium of St. Mokios which may have been a temple of Zeus or Hercules,¹⁶ the three temples on the acropole, of Aphrodite, of Apollo-Helios and of Artemis were left to their prior use and dedication; however, Constantine apparently did discourage pagan worship there.¹⁷

Despite Eusebios’ assertion that Constantine “dedicated the city to the God of the martyrs” building “numerous” churches inside and outside the walls,¹⁸only three churches can be attributed to Constantine:¹⁹ the cathedral basilica, dedicated to Hagia Eirene; a martyrion of St. Akakios, a local martyr, which was located inside the walls and might have been constructed by Constantine; and the church of another local martyr, Mokios, which was situated outside the Constantinian walls, close to a famous cistern. The church of the Holy Apostles (which was located in the area today occupied by Fatih camii) is attributed falsely to Constantine, as he apparently constructed there only a mausoleum for himself.²⁰