The Indo-Europeans originated from the steppes north of the Caucasus Mountains between the Black and Caspian Seas. They were semi-nomadic herders of cattle, sheep, and goats, and some of the earliest to domesticate horses. By around 2000 BC, one group known as the Hittites had migrated to Anatolia in modern-day Turkey and established the capital city of Hattusas, adopting local languages and customs while maintaining their own. Around the same time, another Indo-European group known as the Aryans entered northern India, establishing a rigid caste system that divided society into priests, warriors, traders/landowners, and laborers.