the hejaz area became an important center as islam rose in the 620s. after prophet muhammad of the quraysh tribe started calling to islam in 610, the already existing cities of medina (formerly called "yathrib") and mecca eventually became the holiest places of islam and thus most of muslims. the number of followers rapidly began to grow after the migration (or hijra) of muhammad and his companions in 622 from mecca to medina. during the completion of the religion, both these cities became the holiest places in the muslim world. masjid al-haram and al-masjid al-nabaw i am the main locations of pilgrimage where muslim hopes to visit the kaaba primarily in masjid al-haram and the prophet's tomb in al-masjid al-nabawi at least once in their lifetime.