Kōgen

was a after Kenchō and before Shōka. This period spanned the years from October 1256 to March 1257. The reigning emperor was .

Change of era

• 1256 : The new era name was created to mark an event or a number of events. The previous era ended and a new one commenced in Kenchō 8.

Events of the Kōgen era

• September 1, 1256 (Kōgen 1, 11th day of the 8th month)<!-- NengoCalc 康元一年八月十一日 -->: Kujō Yoritsune, also known as Fujiwara Yoritsune, died at the age of 39 years.
• October 14, 1256 (Kōgen 1, 24th day of the 9th month)<!-- NengoCalc 康元一年九月二十五日 -->: Yoritsune's son and successor as Kamakura shōgun, Kujō Yoritsugu, also known as Fujiwara Yoritsugu, died at the age of 18 years.