Muslims believe that Abraham—known as Ibrahim in the Islamic tradition—and his son, Ismail, constructed the Kaaba. Tradition holds that it was originally a simple unroofed rectangular structure. The Quraysh tribe, who ruled Mecca, rebuilt the pre-Islamic Kaaba in c. 608 CE with alternating courses of masonry and wood. The Hajj (Arabic: حَجّ Ḥaǧǧ ) "pilgrimage"; sometimes also spelled Hadj, Hadji or Haj in English) is an annual Islamic pilgrimage to Mecca, Saudi Arabia, the holiest city for Muslims. Hajj is a mandatory religious duty for Muslims that must be carried out at least once in their lifetime by all adult Muslims who are physically and financially capable of undertaking the journey, and can support their family during their absence. In Islamic terminology, Hajj is a pilgrimage made to the Kaaba, the "House of God", in the sacred city of Mecca in Saudi Arabia. It is one of the Five Pillars of Islam, alongside Shahadah, Salat, Zakat and Sawm. The Hajj is a demonstration of the solidarity of the Muslim people, and their submission to God (Allah). The word Hajj means "to attend a journey", which connotes both the outward act of a journey and the inward act of intentions. Prior to Islam throughout the Arabian Peninsula, the Kaaba was a holy site for the various Bedouin tribes of the area. Once every lunar year, the Bedouin tribes would make a pilgrimage to Mecca. Setting aside any tribal feuds, they would worship their gods in the Kaaba and trade with each other in the city. REF: https://en.wikipedia.org/wiki/Hajj https://en.wikipedia.org/wiki/Kaaba https://www.khanacademy.org/humanities/ap-art-history/introduction-cultures-religions-apah/islam-apah/a/the-kaaba#