Five hundred and fifty-four years ago on this day the Roman Empire was at last extinguished. By then the Empire was, of course, Greek not Roman; Christian not pagan; and no longer strong but pitifully weak. Dispossessed of all its Anatolian and Asian province, and most of its European, all that remained was the great city of Constantinople, much of which was reduced by privation, disease, and depopulation to overgrown ruins. The Turks under a great conqueror, Mehmet II, besieged the city beginning in April, the day after Easter. They outnumbered the defenders at least 10 to 1; possibly the...