Year zero
Year zero does not exist in the anno Domini system usually used to number years in the Gregorian calendar and in its predecessor, the Julian calendar. In this system, the year is followed by . However, there is a year zero in astronomical year numbering (where it coincides with the Julian year ) and in ISO 8601:2004 (where it coincides with the Gregorian year ) as well as in all Buddhist and Hindu calendars.
50 BC
Year 50 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Consulship of Paullus and Marcellus (or, less frequently, year 704 "Ab urbe condita"). The denomination 50 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.