the territory that now constitutes saudi arabia was the site of several ancient cultures and civilizations. the prehistory of saudi arabia shows some of the earliest traces of human activity in the world. the world's second-largest religion, islam, emerged in modern-day saudi arabia. in the early 7th century, the islamic prophet muhammad united the population of arabia and created a single islamic religious polity. following his death in 632, his followers rapidly expanded the territory under muslim rule beyond arabia, conquering huge and unprecedented swathes of territory (from the iberian peninsula in the west to modern-day pakistan in the east) in a matter of decades.