Islam is an Abrahamic monotheistic religion teaching that there is only one God (Allah) and that Muhammad is the last messenger of God. It is the world's second-largest religion, with over 1.9 billion followers, and Muslims form 24.4% of the world's population. Common iconography Colours History Early Islamic armies and caravans flew simple solid-coloured flags (generally black or white) for identification purposes, with the exception of the Young Eagle of Muḥammad, which had the shahada inscribed upon it. In later generations, the Muslim leaders continued to use a simple black, white, or green flag with no markings, writings, or symbolism on it. The Umayyads fought under white and gold banners. The Abbasids chose black (blue) and fought with black banners. The Fatimids used a green standard, as well as white. The Saudi Emirate of Diriyah used a white and green flag with the shahada emblazoned on it. Various countries in the Persian Gulf have red flags. The four Pan-Arab colours, white, black, green and red, dominate the flags of Arab states. Meanings Green – The silk and pillows of Jannah are believed to be green. White – Considered the purest and cleanest color in Islam and the color of the flag of Muḥammad, the Young Eagle. Black – The color of Jahannam as well as the color of the Black Standard. Black Standard The Black Standard is one of the flags flown by Muhammad in Muslim tradition. It was historically used by Abu Muslim in his uprising leading to the Abbasid Revolution in 747 and is also associated with the Abbasid Caliphate. It is also a symbol and is associated with Islamic eschatology (heralding the advent of the Mahdi). The Black Banner, which is different from the flag used by ISIL. Scholars have interpreted ISIL's use of a similar black flag in attempts to their claim to re-establishing a Caliphate. Other symbols Star and Crescent The crescent is usually associated with Islam and regarded as its symbol. The crescent and star symbol became strongly associated with the Ottoman Empire in the 19th century. By extension from the use in Ottoman lands, It became a symbol also for Islam as a whole, as well as representative of western Orientalism. "Crescent and Star" was used as a metaphor for the rule of the Islamic empires (Ottoman and Persian) in the late 19th century in British literature. This association was apparently strengthened by