When did the caste system evolve into a four tiered hierarchy?

The Caste System in India evolved into a four-tiered hierarchy, known as the varna system, around 1500 BCE to 500 BCE, during the early Vedic period. This categorization was primarily based on occupational roles and societal functions, dividing society into four main groups: Brahmins (priests and scholars), Kshatriyas (warriors and rulers), Vaishyas (traders and agriculturalists), and Shudras (servants and laborers). Over time, this framework became more rigid, leading to the complex caste system seen in later Indian society.