Language & WorldFact
Istanbul is probably just Greek for "in the city".
To Greeks, Constantinople was simply "the City", i Polis. The most likely origin of "Istanbul" is the everyday phrase "stin Poli", "in the city" or "to the city". Fusing articles and particles into place names was common in Greek. The name only became official in 1930, when Turkey asked other countries to use Turkish names.
Useful: Many place names are frozen directions; ask what the name once meant as a sentence.
Source: en.wikipedia.org