More than 1.8 million Muslims have gathered in Saudi Arabia ahead of the Hajj pilgrimage that starts today. Hajj pilgrimage, one of the five pillars of Islam, is undertaken by Muslims during Dhul Hijjah or final month of the Islamic calendar. Hajj will last for five days, ending on August 13, 2019. It is mandatory for all adult Muslims who are physically and financially capable of undertaking the journey.