The Evolution of the Roman Calendar
The Roman calendar was first developed as a lunar calendar, so it was difficult for the Romans to reconcile this with the natural solar year. In 45 BC, Julius Caesar reformed the calendar, creating a solar year of 365 days with leap years every four years. This article explains the process by which the Roman calendar evolved and argues that the reason February has 28 days is that Caesar did not want to interfere with religious festivals that occurred in February. Beginning as a lunar calendar, the Romans developed a lunisolar system that tried to reconcile lunar months with the solar year, with the unfortunate result that the calendar was often inaccurate by up to four months. Caesar fixed this by changing the lengths of most months, but made no change to February because of the tradition of intercalation, which the article explains, and because of festivals that were celebrated in February that were connected to the Roman New Year, which had originally been on March 1.