 This caused the calendar to become out of step with the seasons; for example, Caesar's crossing of the Rubicon in January 49 BCE actually took place in mid-autumn.Under his authority as Pontifex Maximus, Gaius Julius Caesar introduced the calendar reform that created the Julian calendar, with a fault of less than a day per century, and which remained the standard till the Gregorian reform in the 16th century.After Julius Caesar's assassination in 44 BCE, his ally Marcus Aemilius Lepidus was selected as Pontifex Maximus.