A crescent moon embracing a single star adorns the flags of a number of modern nation-states with majority Muslim populations. The sign is almost certainly not of Arab origin, and the Ottoman Turks may have appropriated the symbolism from Byzantium. At first, the symbol appeared on the flags of lands formerly under Ottoman rule, but other states with no historical connection to the Ottoman empire have also adopted the imagery.Popular understanding of the symbol usually identifies the crescent moon as the essential indicator of the beginning of Ramadan, the ninth lunar month. More generally still, the symbol reminds some of the lunar cycles that regulate Islam’s religious calendar. Appearing frequently at the top of domes and minarets, the symbol has become a generic reminder of Islam, much the way the cross has for Christianity and the six-pointed star for Judaism.