Short answers, pulled from the story.
Constantinople was founded in 324 by the Roman emperor Constantine I on the site of the existing city of Byzantium, a Greek settlement established around 657 BC. It was formally consecrated and renamed on the 11th of May 330, and on the same date dedicated to Constantine.
Constantinople served as the capital of the Roman Empire from 330 and the Eastern Roman (Byzantine) Empire from 395 until 1453. Its position at the crossing of Europe and Asia, commanding trade routes between the Aegean and the Black Sea, made it the largest and wealthiest city in Europe from the mid-5th century to the early 13th century.
Constantinople fell on the 29th of May 1453 after a seven-week siege led by 21-year-old Ottoman Sultan Mehmed II. The siege began on the 6th of April 1453, and the city was defended by fewer than 8,000 men against Ottoman forces equipped with a cannon built by the Hungarian gunsmith Urban. Mehmed had sealed the city's supply routes the previous year by constructing the Boğazkesen fortress at the narrowest point of the Bosphorus.
In April 1204, armies of the Fourth Crusade breached the sea walls and pillaged Constantinople for three days. The attack was organized by Philip of Swabia, Boniface of Montferrat, and the Doge of Venice. Ancient artworks were destroyed or melted for coinage, the Imperial Library's more than 100,000 volumes were lost, and the city's population of roughly 400,000 was left with about one third homeless.
Constantinople was officially renamed Istanbul on the 28th of March 1930, following the establishment of the Republic of Turkey in 1923 and a formal change to the Turkish alphabet in 1928. The Eastern Orthodox Church continues to use the name Constantinople in the formal title of the Ecumenical Patriarch.
The Theodosian Walls were triple fortifications built in 413-414 AD by Emperor Theodosius II, rising to 18 metres with a moat and palisades in front. They protected Constantinople from Arab sieges in 674-678 and 717-718, and remained unbreached for nearly nine hundred years until the Ottoman conquest in 1453, when a Hungarian-built cannon finally overcame them.