"There is no doubt in the sanctity of Mecca, but a donkey won't become a Hajj pilgrim by just going through the motions." (Rahman Baba)
The reason for the existence of most of the world's cities is obvious to the student of geography. New York and Shanghai control deep ports and straddle great rivers, bringing trade from the interior; Paris and London are at the crossing points of major cross-country rivers; Johannesburg sits atop a great mountain of gold ore; and Moscow and Madrid are at the heart of their great nations, easily able to control even the more distant corners of the land.
Mecca, however, is different, as the city exists solely because it is holy. Even centuries before the birth of the Prophet Muhammad, the leaders of Mecca established that their city was the pre-eminent holy site in western Arabia and established a truce for pilgrims to the city. One effect of this was that Mecca became a center for what might today be described as tourism, as even ancient visitors needed places for food, water, and sleep. At the same time, they could make offerings in the temples and leave with mementos of their time in Mecca. Many also found it convenient to bring their trade goods to the markets of Mecca, where they could find visitors bringing interesting wares from across the region, and the city also enjoyed the status of a trade center.
Of course, Mecca is now best known for being Islam's holiest city, revered as the birthplace of Muhammad and the site where Allah first revealed the Qu'ran to him. Within Mecca is the Ka'aba, a building housed within the Al-Masjid al-Haram (Great Mosque) that is considered the holiest site. Wherever they are in the world, Muslims face in the direction of the Ka'aba while praying.