The Chodoin was a state chamber of the Greater Imperial Palace (called daidairi) in the palace in the ancient times.
The origin of the Chodoin, the most important facility in the daidairi, can be traced back approximately to Emperor Suiko's Oharida Palace, which consisted of the three palaces: the daigokuden (council hall in the imperial palace), the chodo (the Imperial Court), and the choshuden (waiting hall for officials in the imperial palace). The emperor's Imperial throne called 'Takamikura' was placed in the daigokuden, the main hall of the palace, and the emperor was seated on it when attending a ceremony or granting an audience. The courtyard (called 'chotei') down from the daigokuden was lined with the chodo on its both sides, and on its south end were the east choshuden and the west choshuden. The chodoin in Heijo-kyu Palace is said to have been strongly influenced by the gangenden (council hall) in Taimeikyu Palace in Chang'an city.
The chodoin were also called 'Hasshoin;' they were originally administrative offices where government officials in Hassho (eight ministries and agencies) administered the government and the emperor made the final decision
After the peak period of Fujiwara-kyo (the Fujiwara Palace; the ancient capital of Fujiwara), the center of political and general affairs had gradually shifted from the chodoin to the kanga (government office) around them, and by the time of Heian-kyo (the ancient capital of Japan in current Kyoto), the scale of the chodoin had been reduced; as such, the chodoin came to be used mainly for rituals and ceremonies of the Imperial Court such as Choga (New Year's greetings or well-wishes offered by retainers to the Emperor), enthronement and a banquet. Although they were the main facility in the daidairi, the chodoin were often burned down.
However, they were never rebuilt, after the burning down in 1177 in the Heian period, and then their roles were handed down to the dairi, emperor's private houses, and the temporary dairi called 'sato-dairi.'
Incidentally, the current Takamikura is in the shishinden in Kyoto Imperial Palace.
The Heian-jingu Shrine, founded in1895, was a reconstruction of the chodoin in Heian-kyo on a smaller scale, and the main gate of the chodoin such as Oten-mon Gate and daigokuden were restored with the bright red colorant of Bengala, tiled roofs, foundation and pillars.