from the Hejaz region of the peninsula, before expanding into Jordan and southern Israel. On 9 June 2020, the discovery of a 35-metre-long triangular megalithic monument in Dumat al-Jandal, dated back to the seventh millennium BC, presumably dedicated to ritual practices, was published in the journal Antiquity. Archaeological researchers from France, Saudi Arabia, and Italy, headed by Olivia Munoz, believe that these findings illuminate a pastoralist nomadic lifestyle and a ritual used in prehistoric Arabia. In May 2021, archaeologists announced that a 350,000-year-old Acheulean site named An Nasim in the Hail region could be the oldest human habitation site in northern Saudi Arabia. The site was first discovered in 2015 using remote sensing and palaeohydrological modelling. It contains paleolake deposits related to Middle Pleistocene materials. 354 artefacts discovered by researchers, including hand axes, stone tools, and flakes, provide information about tool-making traditions of the earliest living humans inhabiting southwestern Asia. Besides, Paleolithic artefacts are similar to material remains uncovered at the Acheulean sites in the Nefud Desert. Spread of Islam Muhammad, the Prophet of Islam, was born in Mecca in about 570 and first began preaching in the city in 610, before migrating to Medina in 622. From there, he and his companions united the tribes of Arabia under the banner of Islam and created a single Arab Muslim religious polity in the Arabian Peninsula. Following Muhammad's death in 632, Abu Bakr became leader of the Muslims as the first Caliph. After putting down a rebellion by the Arab tribes (known as the Ridda wars, or "Wars of Apostasy"), Abu Bakr attacked the Byzantine Empire. On his death in 634, he was succeeded by Umar as caliph, followed by Uthman ibn al-Affan and Ali ibn Abi Talib. The period of these first four caliphs is known as the Rashidun or "rightly guided" Caliphate (al-khulafā' ar-rāshidūn). Under the Rashidun Caliphs, and, from 661, their Umayyad successors, the Arabs rapidly expanded the territory under Muslim control outside of Arabia. In a matter of decades, Muslim armies decisively defeated the Byzantine army and destroyed the Persian Empire, conquering huge swathes of territory from the Iberian peninsula to India. The political focus of the Muslim world then shifted to the newly conquered territories. Nevertheless, Mecca and Medina remained the spiritually most important places in the Muslim world. The Quran requires every able-bodied Muslim who can afford it, as one of the five pillars of