The author of the calendar was the Greek astronomer Sosygenes and it was introduced in 45 BC. The calendar established a year of 365 days with an additional leap day every 3 years. It was not until 8 AD that a leap year was introduced every 4 years. Before the introduction of the Julian calendar, there was a 304-day Roman calendar, which separated the previous year from the next with a 61-day winter period.
