Final answer:
The highest tier in the Indian caste system was occupied by the Brahmins. They held the highest status in the Vedic society established by the Aryans and had authority over religious rituals and practices being knowledgeable in the Vedas.
Step-by-step explanation:
The group that occupied the highest tier in the Indian caste system were the Brahmins. This is illustrated within the historical context where the Vedic religion of the Aryans led to the creation of a strictly hierarchical society, with the Brahmans at the apex. They are followed by Kshatriyas, the warrior and aristocratic class, then Vaishyas, the merchant and farmer class, and at the lower tier, the Shudras, the worker and laborer class. Below this four-tier system were the Dalits or 'untouchables', considered outside the traditional caste hierarchy. The caste system was enforced through religious principles and has historical roots going back to the Aryan migrations and the subsequent Vedic period in ancient India. The Vedas, sacred hymns brought by the Aryans, became a significant part of the Brahmin authority and the caste system as a whole, emphasizing the religiously sanctioned order of society.