The history of Europe can be traced back to the appearance of the first modern humans identified as ancestors of contemporary Europeans about 37,000 years ago during the Paleolithic. Early European Farmers migrating from Anatolia spread agriculture across the continent during the Neolithic, a period that also included early metallurgy. Starting around 4000 BC, westward migrations of steppe pastoralists spread Indo-European languages. The rise of the city-states of ancient Greece defines the beginning of classical antiquity. The Hellenistic period began with Alexander the Great's 4th-century BC conquests from Greece to India and ended with the Roman Empire's control of the entire Mediterranean basin. Christianity emerged under Roman rule in the 1st century AD. The Migration Period of the Germanic peoples began in the late 4th century AD.