The three holiest sites in Islam are the Masjid al-Haram, or Grand Mosque, (in Mecca) ; the Al-Masjid al-Nabawi, or Prophet's Mosque, (in Medina)and Al-Aqsa Mosque in Jerusalem. Every year millions of Muslims from all over the world visit Masjid al-Haram and Al-Masjid al-Nabawito perform Hajj. Muslims are also required, if physically able, to undertake a pilgrimage to Mecca at least once in one's life: it is strongly recommended to do it as often as possible, preferably once a year.