On March 28, 1930, the Turkish Post Office officially adopted 'Istanbul' in place of 'Constantinople' and other historic names, following a directive under Atatürk's reforms. The change reflected a broader effort to sever ties with the Ottoman and Byzantine past and forge a modern Turkish national identity. Foreign postal services were told to update their records or risk having mail returned.
The city had accumulated names for over 1,500 years—Byzantium, Constantinople, Kostantiniyye—each layer reflecting a different empire's claim on the strategic waterway between Europe and Asia. By 1930, the seven-year-old Republic of Turkey was busy erasing imperial vocabulary wherever it could: the fez was banned, the Arabic script gave way to a Latin alphabet, and now the old capital's name followed suit.
Istanbul itself likely derived from the Greek phrase 'eis tin polin' ('to the city'), a name locals had used colloquially for centuries even while Constantinople remained official abroad. The government's 1930 postal decree simply made formal what many Turks already said informally.
The rebranding became internationally famous decades later thanks to the 1953 novelty song 'Istanbul (Not Constantinople),' which cheerfully mangled the history for pop audiences. But the underlying story was serious: a nation deliberately renaming its most storied city to signal a decisive break from empire and religion-based rule toward secular nationhood.