1799 ( MDCCXCIX ) was a common year starting on Tuesday of the Gregorian calendar ?and a common year starting on Saturday of the Julian calendar , the 1799th year of the Common Era (CE) and Anno Domini (AD) designations, the 799th year of the 2nd?millennium , the 99th year of the 18th?century , and the 10th and last year of the 1790s decade. As of the start of 1799, the Gregorian calendar was 11 days ahead of the Julian calendar, which remained in localized use until 1923.