Daidairi is an Imperial Palace in the ancient capital of Heian. After the 12th century, it often meant a particular Palace where emperor stays within the Imperial Palace as 'Daidairi,' but after the 14th century, the whole Imperial Palace was called 'Daidairi' and the usage of this expression became common. The Daidairi is located in the center of the north end of the ancient capital of Heian.
The Palace was burnt down either due to a political incident or there some accidental fire, it has not been rebuilt since middle of the Heian period. This was an area about 1.2 kilometers long running east to west, and 1.4 kilometer long in North to South, and it was provided with an administration institute and a national ceremony, facilitated yearly events, and it also had a Palace where the emperor lived. There were villas for the government officials and their families inside the Daidairi, and those villas were connected with a corridor to the Seiryoden (name of one of the Imperial Palaces during the Heian period) inside the palace.
There was a large fence made as a roofed mud-wall around the Daidairi, of which the outside fence was called 'Miya-mon Gate' or 'Tonoe.'
The Miyagi-mon Gate was the furthest outside gate, just outside was called the Miya-mon gate, the gate for the inside fence was called the Ko-mon Gate.
The name of the Miyagi-mon Gate inside the Daidairi
Suzaku-mon Gate, Koka-mon Gate, Bifuku-mon Gate on the south side
Anka-mon Gate, Ikan-mon Gate, Tacchi-mon Gate on the north side
Joto-mon Gate, Yomei-mon Gate, Taiken-mon Gate, Ikuho-mon Gate on the east side
Josai-mon Gate, Inpu-mon Gate, Soheki-mon Gate, Danten-mon Gate on the west side
The above gates were established. (Please refer to the images of Heiankyo map.png.)
Out of above gates, Joto-mon Gate and Josai-mon Gate were called 'Tsuchi no mon' (the gate made out of mud), 'Tsuchimikado,' since they had a tile-roofed mud wall without having proper roof to use as service entrance for Okura. (the Ministry of finance)
The name of the street just outside of this gate is 'Tsuchimikado Avenue,' which the surname of the Tsuchimikado family and Fujiwara family's mansion, Tsuchimikado dono (mansion) belong to this name of the place.
The twelve gates excluding Joto-mon Gate and Josai-mon Gate, were called 'The Twelve Gates of the Imperial Palace.'
By the way the Kyoto Imperial Palace where the Emperor lived until the last days of the Edo bakufu (Japanese feudal government headed by a shogun), was established as the Imperial Palace by Emperor Kogon in 1331, where the Emperor used to use Tsuchimikado Higashi Toin Palace as his Satodairi (temporally palace). In 1855 this palace was built under Ritsuryo Style (a system of centralized government based on ritsuryo codes) having Sadanobu MATSUDAIRA (he was not the same famous person as a Senior Councilor in the Kansei Reforms) as Sobugyo (Grand Magistrate).
In 1895 the Heian-Jingu Shrine was built, restoration was done on the facilities like; Daigoku-den building, Oten-mon Gate and Daidairi Chodoin (a large main hall of Daidairi) in small scale than original ones inside the Palace.
The main facilities of the Daidairi
Burakuin: located west of Chodoin, it was used to hold the Sechie event (official events of the Imperial Palace) or to welcome delegates from overseas.
Efu (Security office)
The Imperial Palace
Shishin-den Hall: the main hall of the Imperial Palace
It was changed to the Daigokuden building after the mid Heian period and was used as a place to hold ceremonies, government affairs, or as a place for the Emperor to see people.
Seiryo-den: the Palace where the emperor lives
Koryo-den (one of the palaces within the Imperial Palace where Nyogo live)
Jiju-den (Ninju-den): This Palace is used for watching Sumo games or for the emperor's private functions like the coming-of-age ceremony.
Shokyo-den (the palace used to hold private parties)
Kurodo Dokoro Tsumesho (the station for the office of the court state)
Shunkyo-den: the station for the page
Togu (the Crown Prince's Palace)
Kokyu (the Inner Palace)
Koki-den (the Palace for the Empress, Chugu (second consort of an emperor, Nyogo)
The Palace of Empress, Jonei-den
En no Matsubara: unused land located west of the Palace originally land used to rebuilt the Imperial Palace.
The Grand Council of State
An official in charge of matters relating to Shintoism
Eight Ministries: Nakatsukasa-sho Ministry (the official position to closely serve the emperor and assist issuing the emperor's orders, etc.), Shikibu-sho Ministry, (the official position in charge of personnel), Jibu-sho Ministry, (the official position in charge of surname, succession of the family or marriage, funerals of government officials), Minbu-sho Ministry (the official position in charge of family registration, looking after mountains and rivers, taxes, etc.), Hyobu-sho Ministry (the official position in charge of the military), Gyobu-sho Ministry (the official position in charge of crimes and court), Okura-sho Ministry (the official position in charge of finances), Kunai-sho Ministry (the official position in charge of dealing with matters of the Imperial family)
Ryogenokan (official positions which are not covered in the law)