Saudi Arabia has cities that are important to the Muslim religion. Many Muslims from around the world visit Mecca in Saudi Arabia to make a pilgrimage. The pilgrimage is one of the "pillars of Islam". Other big cities are Riyadh, Jeddah and Dammam. The pilgrimage is called hajj in the Arabic language. Somebody who makes a pilgrimage to Mecca is called a "hajj" in the Arabic language. People who are not Muslim are not allowed to enter Mecca.