What was istanbul called before he ottomans conquered the city in the 15th century

It was called Constantinople, named after the Roman Emperor Constantine.  

Istanbul was called Constantinople before the ottomans conquered the city in the 15th century

Explanation:

Istambul is a well-known city in Turkey and now a lot of people don't know that before having this name it was called by the name of Constantinople, the change happens when the ottomans conquered in the year 1453. "Stanbulin," is the Greek for "to the city, when many signs were found on the road directing travelers it was named Islambol.

The correct answer is - c) Constantinople.

Istanbul is a very old city that has had multiple names throughout the history. This city has always had huge importance in the region as it has an excellent strategic location.

The name that Istanbul had before the Ottoman Turks conquered it and renamed it as such, was Constantinople. The name Constantinople comes from the Emperor Constantine, which is considered as one of the greatest emperors of the Eastern Roman Empire, also known as Byzantine Empire.