Πατριαρχικὴ Μεγάλη τοῦ Γένους Σχολή. αωπ.
The Patriarchal Great School of the Nation. 1880.
(ου is written as the ligature ȣ.)
More prosaically, it is now known in English as Phanar Greek Orthodox College, and in Turkish as Özel Fener Rum Lisesi. It was established in 1454 and was the premier institute for schooling of Greek Orthodox students in the Ottoman Empire. The date refers to the current building, which Wikipedia informs me was constructed in 1881–83.
Its fame endures in Greekdom. In fact, the Greek translation of the Police Academy (franchise) films was Η Μεγάλη των Μπάτσων Σχολή: The Great School of the Cops.