What time period we talking about? Constantinople has been through time for more then 2,000 years, Byzantium, Constantinople, Istanbul.
Throughout the roman era it was the biggest trade hub of the east, and was hence forth the capital of the Eastern Roman empire. Which survived for 1,000 years, when Byzantium fell in the 1400's to the ottomans, the ottomans declared Constantinople their capital, and renamed it Istanbul.
