City in Western Saudi Arabia. (Pop. 689,000). The birthplace of Muhammed ( A.D. c.570). Mecca is the holiest city of Islam and is revered as the first city on earth. Non-Muslims are not allowed to enter. The city is completely dependant on the nearly 2 million pilgrims who come to Mecca each year to pray and study Islam. It is compulsory that Muslims go on a hajj to Mecca at some point in their lives.