Daidō (大同?) was a Japanese era name (年号,, nengō,?, lit. "year name") after Enryaku and before Kōnin. This period spanned the years from May 806 through September 810. The reigning emperors were Heizei-tennō (平城天皇?) and Saga-tennō (嵯峨天皇?).
Read more about Daidō: Change of Era, Events of The Daidō Era