Russia operated post offices in parts of the Turkish Empire for several decades, issuing stamps expressly for this purpose from 1863 until 1921.
Some early examples of these stamps have the inscription РОПиТ for the Русское Общество Пароходства и Торговли, or Russian Steam Navigation and Trading Company. Many others were Russian stamps with printed surcharges in para and piastres. Most of these were surcharged in English, though a small number of later ones were in the Cyrillic alphabet and featured further overprints. Finally, there were several stamps with overprints of local city and town names — Constantinople, Jerusalem, et cetera.
The number of stamps used by Russia for its post offices around the Ottoman Empire is large, and with all the surcharges and overprints, the variety can seem endless. Perfect for collectors and other students of history.