The poster draws on the prophecies of the 13th century Greek priest Agathangelos, who foretold the collapse of the Byzantine Empire at the hands of the Ottomans and its eventual restoration centuries later (text at the bottom reads 'A presentation of Agathangelos' prophecy').
There's also a tree visible in what is presumably another reference to an old legend: namely the legendary "Red Apple Tree" to which the Turks will be expelled once the Greeks reconquer the Empire.
The poster was designed by Emmanuel Papantoniou and was one of many similar maps produced around the time of the Balkan Wars/First World War dreaming of a Greek Constantinople:
Greek postcard from the First Balkan War:
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