GREEKS still consider Tuesday an unlucky day. May 29th 1453, was a Tuesday; the day that Constantinople, the place they called—and often still call—the queen of cities, or simply “the city” was overrun by the Ottoman forces that had bombarded its mighty walls for the past 40 days.

In the history of warfare, this was a watershed. It proved that gunpowder could batter down the strongest walls enough to let the attackers in; the age of immobile, iron-clad soldiers defending big stone fortresses was over. But far more was over than that.

The Byzantine defenders and their Venetian and Genoese allies had noticed portents since the lunar eclipse a week earlier. An icon of the Virgin Mary slipped from its platform as it was carried through the city; then a thunderstorm halted the procession. As dusk fell on May 28th, the Emperor Constantine warned his subjects they might have to sacrifice their lives for the faith, family, country and sovereign. The clergy—bitterly divided by doctrine, as Christianity's 400-year-old east-west schism deepened—put aside their differences to hold an evening service in Saint Sophia, the greatest church of eastern Christendom.