A packed house

The Hajj (Arabic: حج‎ Ḥaǧǧ "pilgrimage") is the pilgrimage to Mecca, Saudi Arabia. It is one of the largest pilgrimages in the world, and is the fifth pillar of Islam, a religious duty that must be carried out at least once in their lifetime by every able-bodied Muslim who can afford to do so. The Hajj is a demonstration of the solidarity of the Muslim people, and their submission to God (Allah in the Arabic language).

The pilgrimage occurs from the 8th to 12th day of Dhu al-Hijjah, the 12th and last month of the Islamic calendar. Because the Islamic calendar is a lunar calendar, eleven days shorter than the Gregorian calendar used in the Western world, the Gregorian date of the Hajj changes from year to year. Ihram is the name given to the special spiritual state in which Muslims live while on the pilgrimage.

The Hajj is associated with the life of Islamic prophet Muhammad from the 7th century, but the ritual of pilgrimage to Mecca is considered by Muslims to stretch back thousands of years to the time of Abraham (Ibrahim). Pilgrims join processions of hundreds of thousands of people, who simultaneously converge on Mecca for the week of the Hajj, and perform a series of rituals: Each person walks counter-clockwise seven times around the Kaaba, the cube-shaped building which acts as the Muslim direction of prayer, runs back and forth between the hills of Al-Safa and Al-Marwah, drinks from the Zamzam Well, goes to the plains of Mount Arafat to stand in vigil, and throws stones in a ritual Stoning of the Devil. The pilgrims then shave their heads, perform a ritual of animal sacrifice, and celebrate the three day global festival of Eid al-Adha.

Islam (English  /ˈɪzlɑːm/; Arabic: الإسلام‎ al-ʾislām  IPA: [ʔɪsˈlæːm] ( listen)) is the monotheistic religion articulated by the Qur'an, a text considered by its adherents to be the verbatim word of God (Arabic: الله‎ Allāh), and by the teachings and normative example (called the Sunnah and composed of Hadith) of Muhammad, considered by them to be the last prophet of God. An adherent of Islam is called a Muslim.

Al-Masjid al-Ḥarām (Arabic: المسجد الحرام‎, pronounced [ʔælˈmæsdʒɪd ælħɑˈrɑːm], "The Sacred Mosque") is the largest mosque in the world. Located in the city of Makkah, it surrounds the Kaaba, the place which Muslims worldwide turn towards while performing daily prayers and is Islam's holiest place. The mosque is also known as the Grand Mosque.

The current structure covers an area of 356,800 square metres (88.2 acres) including the outdoor and indoor praying spaces and can accommodate up to four million Muslim worshipers during the Hajj period, one of the largest annual gatherings of people in the world.