A horrible, bloody war fought between ponies over the question of the appropriateness of inserting additional months into the calendar to keep the months synchronized with their traditional agricultural associations in spite of the discrepancy between the length of the calendar year and the length of the astronomical year. Among the Pro-intercalarians, there were also secondary disputes on who should be in charge of declaring intercalaries, and how often they should be applied. The Anti-intercalarians had their own dispute over whether or not the holidays should be moved, and, if so, if they were to be recomputed every year as a matter of course or not.
The terrible suffering of the Itercalary Wars were only ended when mages devised means of preturbing the motions of the sun and moon with magic, thereby allowing their movements to be made to conform to the idealized calendar. When the world thus almost literally began to revolve around ponies, it was marked by later historians as the beginning of the Classical Period of pony history.