On the other hand, traces of settlement in about 3rd millennium B.C have been uncovered in excavations near the apex of the Golden Horn and in the Asiatic part of the city.
For a few centuries following its establishment, Istanbul existed as a sea port and centre of trade, sovereign for some periods and under the control of superior powers dominating the region the rest of the time. In this period, the city had its acropolis at the site where The Topkapi Palace stands today, and a busy port was situated at the well-sheltered entrance of the Golden Horn. The strong city walls started at the port and, running along the outskirts of the settlement area, reached the Sea of Marmara. Istanbul retained this outlook during the rule of the Roman Empire until the year A.D. 191 when the city took sides with what apparently was the wrong party in a dispute over the throne of the empire. After a siege that lasted for more than two years, it was conquered and razed to the ground by the Roman Emperor Septimius Severus. The city was later rebuilt by the same emperor as a larger city with new city walls and many new buildings.

The Roman land walls: 5th century A.D. This formidable defense system, more than 6 kilometres long with 96 towers, effectively stopped all invaders until the Turkish Conquest in 1453.
In the 4th century, the Pax Romana had expanded to such a wide area that the city of Rome, its capital, no longer had a central location. Emperor Constantine the Great who observed the problems this situation caused recognized the advantages offered by Istanbul's location, at the crossroads of the major land and sea routes of the time and its mild climate and consequently named the city as his new capital. This triggered rapid development in the city.
A new line of city walls were built in about six years so that the city could expand comfortably, and a number of temples, palaces, official buildings, baths and a hippodrome were constructed. In A.D. 330 with great fanfare, the city was officially proclaimed to be the capital of the Roman Empire.
During the golden age that began with this event, the city was first called Deutera Roma (the Second Rome) or Nea Roma (the New Rome), but these two names were soon given up and replaced by Byzantium which was used until many centuries later when "Constantinopolis" (or "Polis" for short among the common folk) became the fashion for a time.
The emperors succeeding Constantine carried on with the effort to beautify and improve the city and had new buildings, avenues, aqueducts an monuments built for this purpose. The first churches of the city were also constructed during this period.
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