Istanbul was founded in the 7th century BC on a naturally defensive site from which trade along the Bosphorus could be . controlled. For 16 centuries it was a great imperial capital, first of the Byzantine Empire and then of the Ottoman sultans. Some knowledge of the histories of these two civilizations helps the visitor to appreciate the magnificent monuments found throughout the city.

The topography of Istanbul was formed at the end of the last Ice Age, when meltwaters created the Bosphorus. The Stone Age cultures in the area were replaced by Copper Age villages and walled Bronze Age towns (notably Troy, . The Bosphorus was an important trade route in the ancient world along which ships carried wine and olive oil north from the Mediterranean, and grain, skins, wool, timber, wax, honey, salted meat and salted fish south from regions around the Black Sea.
The area around the Bosphorus was subjugated by a series of peoples, starting with the Mycenaeans (1400-1200 BC). Between 800 and 680 BC the region was controlled by the kingdom of Phrygia. Later, in 676 BC, Greek expeditionaries founded the city of Chalcedon (on the site where modern Kadıköy now stands).

THE FOUNDATION OF BYZANTION

The foundation of Istanbul is usually dated to 667 BC when, according to legend, a Greek colonist, Byzas, led an expedition from the overcrowded cities of Athens and Megara to establish a colony on the European side of the Bosphorus. This colony, known as Byzantion, grew to be a successful independent city-state, orpolis, one of the 40 most important such states throughout the Ancient Greek world. During the next few centuries, Byzantion worked in partnership with Chalcedon, using the same coinage and sharing the tolls exacted from passing sea trade.
But Byzantion had to struggle to maintain its independence in the mercurial politics of the ancient world. It endured Lydian (560-546 BC), Persian (546-478 BC). Athenian and Macedonian (334-281 BC) rule before briefly regaining its autonomy. In 64 BC it was subsumed into the Roman Empire as Byzantium. The city was almost destroyed in AD 195 by Septimius Severus because of its support for his rival for the imperial throne, Pescennius Niger. It survived the Goths' devastation of Chalcedon in AD 258 but trade in the region dramatically declined in the following years.   (s1)

THE BYZANTHION PERIOD

There have been settlements in what is now Istanbul since prehistory but the foundation of today's Istanbul were lain in the 7th century BC.
The Megarians came into Istanbul from Greece through the Sea of Marmara in 680 BC They established a colony on the Acropolis above the Golden Horn opposite the Greek Colony of Chalcedon, which had been established a few years earlier. The Chalcedon Colony was involved in architecture and referred to as "the Land of the Blind," possibly because they must have been blind no to see the advantages of setting on the European side of the Bosphorus, which would be much more secure militarily. The Megarians, under the leadership of Byzas, acted according to a Delphic oracle in choosing the site. They were settled in (today's Sarayburnu) and the town came to be called Byzantium. It is thought that various Thracian people were living in the area and intermingled with the Megarians. Byzantium, through becoming a commercial center and as a result of its being easily defensible, became a powerful, fast-growing member of the Greek colonies.
In 513 BC. Byzantine was taken by the Persian leader Darius who had captured Anatolia. The city remained in Persian hands until it was taken by the Spartan general Pausanius in 477 BC. He in turn, set himself up as a tyrant and was driven out by the Athenians and their allies in 475 BC. The city revolted against the Athenians and surrendered to the Spartan commander Lysander in 403 after the final defeat of Athens in the Peloponnesian wars.
The city entered into an uneasy alliance with King Philip of Macedonia (father of Alexander the Great) during which the city wall were repaired but surrendered without a battle to Alexander the Great in 334 BC. After his death m 323, the city was under the leadership of one of the generals of Alexander the Great, Antigonos, but more or less governed itself.
The city was overcome by hordes of Saxons arriving from the West in 278 BC. and was looted and forced to pay tributes. It was later captured by the Allied forces of Rhodes, Pergamum and Bithynia under whose sovereignty it remained until it was bequeathed to the Roman Empire by the last ruler of Pergamum. The Macedonia-Roman wars ended in the sovereignty of Rome over the Balkans, Asia minor and Byzantium in 146 BC. and a period of peace ruled for the next 300 years. ( s2 )