Short answers, pulled from the story.
Greek colonists from Megara established Byzantium on the Sarayburnu promontory around 657 BCE. Modern excavations suggest the name might reflect earlier Thracian settlements, and Pliny the Elder mentioned a Thracian toponym Lygos as an earlier name for the site.
Roman emperor Constantine the Great refounded the city in 324 CE and named it Nova Roma. On the 11th of May 330, Constantinople was proclaimed the capital of the Roman Empire after he effectively became emperor of the whole empire in September 324.
On the 29th of May 1453, Sultan Mehmed II captured Constantinople after a 55-day siege. Hours after the fall, the sultan converted Hagia Sophia into an imperial mosque and declared himself Kayser-i Rûm, the Ottoman Turkish equivalent of the Caesar of Rome.
On the 29th of October 1923, the Grand National Assembly of Turkey declared the establishment of the Turkish Republic with Ankara as its capital. This followed the Treaty of Lausanne signed on the 24th of July 1923 which ended the occupation of Constantinople.
Despite the myth that seven hills make up the city, there are more than 50 hills within the city limits. Aydos is the tallest hill at high elevation, while the North Anatolian Fault under the Sea of Marmara has caused earthquakes in 1766 and 1894.