 Each book covers one month, January through June, of the Roman calendar, and was written several years after Julius Caesar replaced the old system of Roman time-keeping with what would come to be known as the Julian calendar.The popularity and reputation of the "Fasti" has fluctuated more than that of any of Ovid's other works.The poem was widely read in the 15th–18th centuries, and influenced a number of mythological paintings in the tradition of Western art.