The star and crescent is a symbol consisting of a crescent with a star at the concave side. In its modern form, the star is usually shown with five points (though in earlier centuries a higher number of points was often used). Although the two signs together or the crescent only is often regarded as a symbol of Islam, it wasn't until the Ottoman Empire that the crescent moon and star became affiliated with the Muslim world. When the Turks conquered Constantinople (Istanbul) in 1453, they adopted the city's existing flag and symbol. Legend holds that the founder of the Ottoman Empire, Osman I, had a dream in which the crescent moon stretched from one end of the earth to the other. Taking this as a good omen, he chose to keep the crescent and make it the symbol of his dynasty. There is speculation that the five points on the star represent the five pillars of Islam, but this is pure conjecture. The five points were not standard on the Ottoman flags, and it is still not standard on flags used in the Muslim world today.