In the Orthodox Tradition, one does not celebrate the birthday of a martyr or a saint. Rather, one commemorates the day of the subject's death.
Therefore, May 29, 1453 is the day from which to start counting. We are very nearly at the 556th feast in remembrance of the Roman Empire, may its memory be eternal.
However, since in the West birthdays are generally the preferred memorial, and since I live in said West, I will go ahead and humor this thread by saying: "Happy Birthday!" I'd wish for many more, but alas, it has fallen asleep and will (probably) not awake again in this age.
0 Lord, save thy people and bless thine inheritance:
To our Rulers grant victories over the barbarians,
And by thy Cross protect thine own Estate.
- Prayer on the Feast of the Elevation of the Cross (September 14), established by Heraclius, Basileus (610-41), after recovering the True Cross from its captivity by the Persians and the utter defeat of the Sassanians by Roman arms.