Constantinople

Constantinople was the capital of Eastern Rome, Rome was the capital of Western Rome. Therefore they were both capitals. The Emperor Constantine rebuilt Constantinople out of Byzantium and, being an egotistical ruler like most, named it after himself. Constantinople was probably slightly more cultured after the division of the Roman Empire by Diocletian. They were both major cities with Constantinople being a major port and many people wanted control of the strait it was sitting on. Many years before it was Constantinople, the Trojan War broke out over the control of several straits, the one that Constantinople (now Istanbul) sits on being one of them. Anyway, similarities. I suppose the last similarity I can think of would be that they were both major cultural centers and later (like several hundred years later) would become great cities of past, but also still full of splendor and majesty.

Emperor Constantine of Byzantium: By File:Hagia_Sophia_Southwestern_entrance_mosaics.jpg: Photograph: Myrabella derivative work: Myrabella (Public domain or CC0), via Wikimedia Commons
Set up my Roman Emperor Constantine II, the same emperor who legalized Christianity, it was the capital of the Roman Empire's eastern section. Ruling such a large empire from one seat and by one person was hard for the roman empires. rome was the capital of the west, constantinople was capital of the east. AFter the fall of the WEstern Roman empire in the 5th Century AD, Constantinople became the only large power house in europe/middle east. Constantinople controlled most of the ports on the black sea and controlled the trade routes that went from China and India to Western Europe.
The Roman Empire (or Byzantine Empire by that point) was crumbling territorially speaking. It had lost land in Levant which is why it called for help from the pope. It was struggling to maintain Asia Minor and was able to maintain the Balkans, but not without some setbacks. Sure the Crusaders sacked Constantinople and took greath wealth from the city, but the Empire did stay afloat for anouther 200 years. I guess it only hasten the eventual collpase.
The reaon why they attacked Constantinople was because the Venetians wanted to make money. The Fourth Crusade was supposed to sail from Venice to Egypt. Problem was that the Venice was a trading city, and it had good buisness relations with the muslims. So they assuered that the crusaders would never arrive. So the venician king made a big party for the knights once they arrived and made them pay an insane amount of money which they could not pay on their own. In debt, they were sent to Constantinople instead, so when they sacked the city, they Crusaders were in fact paying their debt off to Venice.

Aya Sofia in modern city Istanbul once was Constantinople: image uploaded to the German Wikipedia by Robert.Raderschatt (self made) via Wikimedia Commons

In 1453 the Ottoman turks( after hundreds of years of slowly conquering the the Byzantines ) surrounded and conquered constantinople after a 3 month siege by this time all of greece with the exception of the very southern tip called the mistra and that forked shaped pennensula on the eastern side called the pellopenese was alredy controlled by the ottomans. Constantinople was really nothing more than a protectorate of the ottoman empire at the time.
Constantinople was the base for eastern christendom, is located closer to bosphorus strait inside Turkey , Ottomans came from the east and took over, from there and then on Muslims located themselves inside Turkey and then crafted a new empire that strecthed towards south today Lebanon and middle east and then towards the Balklands, today former Yugoslavia, they atempted to conquer Viena ( Austria) but failed, they crafted a large navy got in fight with Greece, tried to conquer Malta and failed, the ruler became known as the sultan Ahmed 6 was the last one, the also had war against Russia during 1860´s with assistance from England, the empire was over as a consequence of the loss of world war one, last sultan was Ahmed 6 ,then after war Mustafa Kemal came and made the new republic.