Which was the language in which Alvars and Nayanars sang hymns in praise of Gods?

Sanskrit Tamil Prakrit Hindi

Tamil

Some of the earliest bhakti movements (c. sixth century) were led by the Alvars (literally, those who are "immersed" in devotion to Vishnu) and Nayanars (literally, leaders who were devotees of Shiva). They travelled from place to place singing hymns in Tamil in praise of their gods.