404 (CDIV) was a leap year starting on Friday of the Julian calendar, the 404th year of the Common Era (CE) and Anno Domini (AD) designations, the 404th year of the 1st millennium, the 4th year of the 5th century, and the 5th year of the 400s decade. As of the start of 404, the Gregorian calendar was 1 day ahead of the Julian calendar, which was the dominant calendar of the time.

• January 1 – Last gladiator competition in Rome.
• Atticus of Constantinople becomes Patriarch of Constantinople.
• Honorius moves the capital of the Western Roman Empire to Ravenna.
• Saint Telemachus matyrdom.