What do you call a city so big it doesn't need a name? Greeks had an answer: the City.
From about 400 AD, that was the word for Constantinople: hē Polis. Which city? There was only one. Greeks still say i Poli today.
Say it quickly, the way people do: stin Poli. "In the City."
Around 956, an Arab traveller called al-Masudi wrote down what he heard Greeks saying: stan būlin. That is the oldest record of the name, and the leading explanation of where it comes from. It isn't Turkish or Latin. It's Greek, as an Arab heard it.
Turkish ears took it as a name and put a vowel in front, because Turkish doesn't start words with st. İzmit and İznik got the same treatment. That gives you İstanbul.
Here's the part people miss. The Ottomans never dropped the old name. Coins and court papers said Kostantiniyye. Everyone else said İstanbul, and at first it meant only the walled old city. The city carried both names for centuries.
So did 1930 "rename" it? Depends who you ask. Popular accounts point to a postal law of 28 March 1930: letters addressed to Constantinople would be sent back. One analyst says there was never a law at all, only a postal circular, because Istanbul was already the name. What's certain: from 1930 Türkiye asked the world to use Turkish place names, and the US State Department switched that May.
A Greek nickname some sixteen centuries old, and a famous renaming that may never have happened.
Sirkeci's Grand Post Office (Büyük Postane) was finished in 1909 and still works as one, with a postal museum inside. Go on a weekday morning, write a postcard, and watch the stamp land: İstanbul. The museum's hours weren't confirmed when we checked, so look before you go.
