Gundan (army corps) (in ancient Japan) (軍団 (古代日本))

Gundan refers to a military organization established around the country under the ritsuryo system (the system of centralized government based on the ritsuryo code) in ancient Japan. Gundan was individually called by attaching a name of place to 'Gundan' such as Tamatsukuri Gundan (army corps in Tamatsukuri-gun, Mutsu Province), or to 'dan' like 'Tamatsukuri dan' (same meaning as the Tamatsukuri Gundan).

Gunboryo (the Statute on Military Defense) under the Yoro ritsuryo code regulated that every 3rd Seitei (a man in good health between 21 and 60 years of age) was requisitioned as a soldier. Under this statute, one third of the population of Seitei in the nation was obliged to work in Gundan, but the actual number of soldiers inducted seemed to be smaller than that, and it is considered that, in fact, one Seitei was inducted from one Ko (smallest organization unit in provincial administration).

Soldiers had to provide themselves with food and weapons, and in normal times, they were alternatively on duty and in charge of training and guard.

Scale and chain of command
Gundan in normal times was put under the control of Kokushi (provincial governor). A standard gundan had 1,000 soldiers, but Gundan in a smaller province had fewer soldiers than that. In that case, the appropriate scale of gundan seemed to be organized in units of 200 soldiers as 800, 600 and 400 soldiers. However, in Mutsu Province, 1 Gundan seemed to have more than 1,000 soldiers at one period.

Gundan having 200 or 400 soldiers was headed by 1 Shoki (deputy commander).

Gundan having 600 or 800 soldiers was headed by 1 Daiki (chief commander).

Gundan having 1,000 soldiers or more was headed by 1 Daiki and 2 Shoki.

Gundan contained the following officers. Koi (commissioned officer) headed 200 hundred soldiers. Koi was also called Nihyakucho (head of unit having 200 soldiers).

Ryosui headed 100 soldiers.

Taisei headed 'Tai' (corps) consisting of 50 soldiers. Taisei was also called Taicho.

Kacho headed 'Ka' (one of the units of corps; literally meaning "fire") consisting of 10 soldiers. Ka' refers to a minimum unit of supply in the soldier's living and right path, and probably originated from the event that meals for 10 soldiers were made with 1 fire.

There is a theory that Gocho headed 'Go' (one of units of corps; literally meaning "five") consisting of five soldiers, but some people doubt of its existence because there were no definite regulations and there were no descriptions of its existence in found materials.

Daiki - Shoki - Koi - Ryosui - Taisei - Kacho - (Gocho)

One Gundan was deployed at least in one province, and more than one Gundan was deployed in a larger province. The chain of command in Gundan responded to a local organization below Gun (county), and Daiki and Shoki who were commanders were selected from the class of Gunji (local magistrates). Gundan existed as one for several counties, stationed near Gunke (public office), and engaged in training.