The Vedic beliefs and practices of the pre-classical era were closely related to the hypothesised Proto-Indo-European religion, and the pre-Islamic Indo-Iranian religion. The earliest iconic artworks of Shiva may be from Gandhara and northwest parts of ancient India. There is some uncertainty as the artwork that has survived is damaged and they show some overlap with meditative Buddha-related artwork, but the presence of Shiva's trident and phallic symbolism in this art suggests it was likely Shiva. Numismatics research suggests that numerous coins of the ancient Kushan Empire that have survived, were images of a god who is probably Shiva. The Shiva in Kushan coins is referred to as Oesho of unclear etymology and origins, but the simultaneous presence of Indra and Shiva in the Kushan era artwork suggest that they were revered deities by the start of the Kushan Empire.