The Imperial Palace East Gardens (Kokyo Higashi Gyoen) are a part of the inner palace area and are open to the public. The East Gardens are the former site of Edo Castle’s innermost circles of defense, the honmaru (“main circle”) and ninomaru (“secondary circle”). None of the main buildings remain today, but the moats, walls, entrance gates and several guardhouses still exist.
Edo Castle was the residence of the Tokugawa shogun who ruled Japan from 1603 to 1867. Emperor Meiji also resided there from 1868 to 1888 before moving to the newly constructed Imperial Palace.- japan-guide.com