The 20,000 square metres area surrounded by the inner moat is called the honmaru. At the time of construction, the honmaru palace was of a similar scale to the ninomaru palace and sliding door paintings of the Kano school decorated the inside. Also, in the honmaru a five-storied castle tower stood, however was lost to fire after a lightening strike in 1750, and following that the palace was lost to fire after the great fire of Kyoto city in 1788.
Following that reconstruction of the honmaru palace did not occur for a long time, but the honmaru palace was built for the 15th Tokugawa shogun, Yoshinobu, as a residence during the final days of the Tokugawa shogunate, but was then dismantled in 1881. The present-day honmaru palace is the old Katsura-no-miya Palace which was located through the Imadegawagomon Gate of the Kyoto Imperial Gardens, and was moved to the grounds of the honmaru from 1893 to 1894. When the Katsura-no-miya Palace was still located within Kyoto Imperial Palace, before Emperor Ninko’s daughter, Princess Kazunomiya was married to the 14th Tokugawa shogun, Iemochi, the building had been lived in for about one year and eight months. When the Imperial Palace went up in flames in 1854 it escaped the fire and is a building of deep history that was used as a temporary palace of Emperor Komei.