Periodization
The adoption of the Sexegenary cycle calendar (Jikkan Jūnishi) in Japan is attributed to Empress Suiko in 604; and this Chinese calendar continued in use throughout the Temmu period.
In 645, the system of Japanese era names (年号,, nengō,?, lit. "year name") was introduced. However, after the reign of Emperor Kotoku, this method of segmenting time was temporarily abandoned or allowed to lapse. This interval continues during the Temmu period.
Neither Emperor Temmu's reign nor the Temmu periodization are included in the list of nengō for this explicit duration of time. The Hakuhō period (白鳳時代, hakuhō jidai?, lit. "white phoenix") was an unofficial nengō during the reign of Emperor Temmu after Hakuchi and before Suchō. The duration of this discrete non-nengō timespan lasted for 15 years.
In the post-Taika or pre-Taihō chronology, the first year of Emperor Temmu's reign (年号天皇元年 or 年号天皇1年) is also construed as the first year of the Temmu period (年号1年).
Read more about this topic: Temmu (period)