The most sacred place in Islam is the Ka'ba in Mecca, Saudi Arabia. The Ka'ba is a mosque which was built by Abraham around a black stone. The Prophet Muhammad designated Mecca as the holy city of Islam and the direction that all Muslims should offer their prayers.
The second holiest site in Islam is Medina, the "City of the Prophet." It is in the Hejaz region of western Saudi Arabia. It was to Medina city where Muhammad fled when he was initially driven out of Mecca, and the place where he attracted his first followers. Medina currently has a population of about 600,000 people and is the home of "The Prophet's Mosque."
The third most sacred city in Islam is Jerusalem. Jerusalem is revered because, in Muslim tradition, Muhammad miraculously traveled to Jerusalem by night and ascended from there into heaven. The two most important Muslim sites in Jerusalem are the Dome of the Rock and the Al-Aqsa Mosque.
Karbalā' is a city in Iraq, located about 100 km southwest of Baghdad at 32.61°N, 44.08°E. The capital of Al Karbala Province, the city of Karbala had an estimated population in 2003 of 572,300 people. Shi'a Muslims consider Karbala to be one of the holiest places in the world, second only to Mecca and Najaf.
Najaf is a city in Iraq, about 160 km south of Baghdad, located at 31.99°N 44.33°E. The capital of Najaf province, the city of Najaf had an estimated population in 2003 of 585,600 people. Najaf is one of the holiest cities in Shi'a Islam and is the center of Shi'a political power in Iraq.