Simplify the following text for a Grade 10 native English-speaking person.
Original: Year 1813 ( MDCCCXIII ) was a common year starting on Friday ( link will display the full calendar ) of the Gregorian calendar and a common year starting on Wednesday of the 12-day slower Julian calendar .
Simplified: Year 1813 ( MDCCCXIII ) was a year starting on Friday of the Gregorian calendar ( or a year starting on Wednesday of the 12-day slower Julian calendar ) .