1657 (MDCLVII) was a common year starting on Monday of the Gregorian calendar and a common year starting on Thursday of the Julian calendar, the 1657th year of the Common Era (CE) and Anno Domini (AD) designations, the 657th year of the 2nd millennium, the 57th year of the 17th century, and the 8th year of the 1650s decade. As of the start of 1657, the Gregorian calendar was 10 days ahead of the Julian calendar, which remained in localized use until 1923.