Historians divide history into two main periods: prehistory and history. Prehistory began with the appearance of the genus Homo around 2.5 million years ago and ended around 3500 BC with the development of writing. Prehistory includes the Paleolithic period of nomadic hunter-gatherers, the Neolithic period of the emergence of agriculture and sedentary communities, and the Metal Ages of metallurgy. History began around 3500 BC with early civilizations like Mesopotamia, Egypt, Greece, and Rome during the period of Antiquity. The fall of the Roman Empire in 476 AD marked the end of Antiquity and the beginning of the Middle Ages.