The final pillar of Islam, Hajj is a pilgrimage to the holy city of Mecca, where Muslims visit the Kaaba, the religion's most holy site, and perform special rites. All Muslims who are financially and physically able to make the journey must do so and it promotes oneness with fellow Muslims, acting as a "common bond among the diverse believers," according to "The Guardian." Performing the Hajj is also an important part of obeying rules laid down by Muhammad.