How did Mithra become associated with contracts and oaths in ancient Iran?

In ancient Iran, Mithra’s association with contracts and oaths was rooted in the very meaning of his name and his function as a celestial overseer of human conduct. The word mithra functioned as a common noun meaning "covenant," "contract," or "treaty," establishing him as the divine guarantor of solemn agreements between individuals, countries, and other sociopolitical entities.1

His role as the god of contracts was reinforced by several key factors:

• Linguistic and Social Ties: The term mitra (in both Iranian and Vedic traditions) could be translated as either "friend" or "contract," reflecting the ancient understanding that mutual obligations and contracts are the foundations of friendship and good relations between people.2
• Divine Oversight: As a deity of light, Mithra was believed to "behold everything." He was described as having 1,000 ears and 10,000 eyes, allowing him to act as a "sleepless" and "ever-waking" guardian who could identify and severely punish any covenant breaker (mithra-drug).12
• Ritual Sanction: Treaties in the ancient world were often sanctioned by a common meal or sacrifice, and Mithra was invoked to witness these oaths, ensuring that the parties involved remained faithful to their promises.23