When composition of "Natural History" began is unknown. Since he was preoccupied with his other works under Nero and then had to finish the history of his times, he is unlikely to have begun before 70. The procuratorships offered the ideal opportunity for an encyclopedic frame of mind. The date of an overall composition cannot be assigned to any one year. The dates of different parts must be determined, if they can, by philological analysis (the "post mortem" of the scholars).