Hajj,a pilgrimage to Mecca, is one of the Five Pillars of Islam (Profession of Faith, Prayer, Fasting, Charity, Pilgrimage) and thus obligatory for all Muslims with the physical and financial ability to make it. Over ten million Muslims visit the city during the month of ''Dhu'l-Hijjah'' yearly. Visits outside this month are known as minor pilgrimages or ''Umrah'', and while not compulsory are strongly encouraged. Pilgrimages to Mecca have been undertaken for over 2000 years. Before the Islamic tradition began, Mecca was visited by Christians and Jews alike as they visited the Kaaba.According to tradition Kaaba was ordained by God to be built in the shape of the House in Heaven called Baitul Ma’amoor(House of the Lord). God in his infinite Mercy ordained a similar place on earth and Prophet Adam and his wife Eve were the first to build this place. The Bible, in the Book of Genesis, describes its building when God ordained Abraham to erect a Shrine for worship, when Abraham was ordered to go to the Southern desert with his wife Hagera and infant son Ishmael. The Old Testament describes this building as the Shrine of God at several places, but the one built at Ma’amoor is very similar to the one at Makka. Scientific evidence proves that the bible was referring to the stone built house at Makka. When Prophet Abraham built the Holy Shrine in Makka, his prayers were that this place should remain a center of worship for all good and pious people (be they Jewish, Christian or soon Muslim) and that God should keep his family the custodians of the Holy place. Ever since, Ishmael the son of Abraham who helped his father to build this place and his descendants remained the custodians of the Holy Shrine. History tells us that centuries passed and the guardianship of the Kaaba remained in the family of Ishmael and the sons of Israel until the coming of Prophet Mohammed. http://wikitravel.org/en/Mecca