The five-day pilgrimage occurs in the final month of the Islamic lunar calendar Karim Sahib/AFP/Getty Images

More than two million Muslim pilgrims will make the journey to the Saudi city of Mecca this week, in what is one of the largest religious gatherings of people in the world. As the fifth and final pillar of Islam, it is a mandatory religious duty for adult Muslims to make the pilgrimage and it must be carried out at least once a lifetime, if an individual is physically and financially able to.

The exact date of the beginning of Hajj depends on the lunar calendar and this year it is expected to start on Friday 9 September and end on Wednesday 14 September. The pilgrimage occurs in the last month of the Islamic calendar, Dhu al-Hijjah.

Muslims of every ethnic group, social status and culture gather together in Mecca and stand before the Kaaba – the most famous shrine in the Muslim world – praising Allah together.

The ritual is designed to promote the bonds of Islamic brotherhood and sisterhood by showing that everyone is equal. In one of the acts of worship, thousands of people move counter-clockwise, seven times, around the Kaaba.

The Hajjis, or pilgrims, wear simple white clothes to perform the same acts of worship and renew their sense of purpose in the world.

To carry out the pilgrimage rituals you need to be in a state of Ihram, or purity, which is achieved by observing several regulations, including abstaining from marital relations, not shaving or cutting nails, refraining from using perfumes and avoiding fighting or arguing. Men must not wear clothing with stitching and women must not cover their faces, even if they would do in their home country.

Pilgrims can also go to Mecca to perform the same rituals at other times of the year, which is sometimes referred to as Umrah or the "lesser pilgrimage".

The Islamic festival of Eid al-Adha occurs on the third day of the Hajj pilgrimage, which this year falls on 12 September. Known as Greater Eid or the Feast of the Sacrifice, it is the second of two major Eid Muslim holidays.