 Of the 18 Mahapuranas (great Puranas), many have titles based on one of the avatars of Vishnu.However, quite many of these are actually, in large part, Shiva-related Puranas, likely because these texts were revised over their history.Some were revised into Vaishnava treatises, such as the "Brahma Vaivarta Purana", which originated as a Puranic text dedicated to the Surya (Sun god).