On the ninth day of the ninth month of August in the ninth year of Wu De (September 4, 626), Li Shimin officially ascended the throne as emperor for Emperor Taizong of Tang. Interestingly, according to historical records, The enthronement ceremony of Tang Taizong was held in the Xiande Hall of the Eastern Palace (Taizong is located in the Xiande Hall of the Eastern Palace). The Eastern Palace is the place where the crown prince lives and works, so why is Tang Taizong's enthronement ceremony held in the Eastern Palace?
Friends familiar with the history of the Sui Dynasty and the Tang Dynasty should know that the Chang'an City of the Tang Dynasty completely inherited the architectural pattern of the Sui Dynasty Daxing City. The Taiji Palace (Taiji Hall) of the Sui Dynasty was also the palace where the Tang Emperor lived and worked in the early years of the Tang Dynasty, and the enthronement ceremony of Tang Gaozu Li Yuan was held in the Taiji Palace (Gao Zu is the emperor located in the Taiji Hall), and the enthronement ceremony of Tang Taizong should also be held in the Taiji Palace.
However, Li Yuan did not willingly pass the throne to Tang Taizong, but Tang Taizong forced Li Yuan to abdicate through the "Xuanwumen Change". Because he was unhappy that his second son had taken the throne, Li Yuan often intentionally or unintentionally blocked Tang Taizong in the years from the "Xuanwumen Revolution" to the fall of the Eastern Turks. Tang Taizong's enthronement ceremony was held at the Crown Prince's Eastern Palace as a result of Li Yuan's deliberate obstruction.
Because the Emperor Taishang belonged to the unconventional existence in ancient China, the power and place of residence of the Emperor Taishang was a "metaphysics", and there were no certain rules at all. Although Li Yuan decided to cede the throne to Emperor Taizong of Tang, he refused to leave the Taiji Palace, where the emperor lived. Tang Taizong, who had already taken the throne and faced many problems, could not force his father to move, so he had to continue to live in the prince's Eastern Palace.
Because of this, Tang Taizong's enthronement ceremony had to be held in the Xiande Hall of the Eastern Palace. Li Yuan, who became emperor of taishang, did not move out of the Taiji Palace until the third year of Zhenguan (629) and moved to the Hongyi Palace (Da'an Palace). The Hongyi Palace was originally the palace of Tang Taizong's Qin Dynasty, so some people in later generations believed that Tang Taizong's father Li Yuan moved to the Hongyi Palace as a suspicion of revenge.