491 (CDXCI) was a common year starting on Tuesday of the Julian calendar, the 491st year of the Common Era (CE) and Anno Domini (AD) designations, the 491st year of the 1st millennium, the 91st year of the 5th century, and the 2nd year of the 490s decade. As of the start of 491, the Gregorian calendar was 1 day ahead of the Julian calendar, which was the dominant calendar of the time.

• March 17 – Saint Patrick, patron saint of Ireland (possibly died this year, could also have died in the year 493)