Rocher states that the date of the Vishnu Purana is as contested as that of any other Purana. References to Vishnu Purana in texts such as Brihadvishnu whose dates are better established, states Rocher, suggest that a version of Vishnu Purana existed by about 1000 CE, but it is unclear to what extent the extant manuscripts reflect the revisions during the 2nd millennium. Vishnu Purana like all Puranas has a complicated chronology. Dimmitt and van Buitenen state that each of the Puranas including the Vishnu Purana is encyclopedic in style, and it is difficult to ascertain when, where, why and by whom these were written: