Ottoman Empire, 1453
Following the conquest of Constantinople, a crescent (and sometimes also a star) was displayed on a green flag. The flag was initially green and only in 1793 was officially changed to red. It was also the flag for the Ottoman Caliphate. It was founded in 1517 and was the last Sunni Islamic caliphate of the late medieval and the early modern era until abolished in 1924. The green crescent flag is often displayed on mosques, with or without the star, in countries that used to be part of the Ottoman Empire. There were various naval flags, some displaying up to three crescents, up to the 19th Century.