Edo Castle has roughly 850 years of history since Edo Shiro Shigenaga of the Edo clan built "Edo residence" advancing into Musashi in the mid-12th century. A singular castle that has lived on through Edo, Ota, Uesugi, Hojo, Tokugawa, and the present Imperial House. The Tokugawa-era castle was Japan's largest megastructure, surpassing Nobunaga's Azuchi and Hideyoshi's Osaka.
Tokugawa Ieyasu, relocated to Kanto, began construction in 1591 while still a great daimyo; becoming shogun in 1603 and opening the Edo shogunate, he, Hidetada, and Iemitsu spent about half a century across three generations investing enormous effort and wealth in a vast castle complex. In 1636 the inner citadel (honmaru, ninomaru, sannomaru, nishinomaru, fukiage, kitanomaru) and outer citadel (Marunouchi, samurai districts, merchant quarters—roughly all present Chiyoda Ward) were complete and Edo Castle's extent fixed.
Built as a "hirayamajiro" using terrain sloping from the Musashino plateau toward Edo Bay, the Edo coastline before Ieyasu lay near present Tamachi, Hibiya, Kasumigaseki, and Shinbashi. Hibiya Inlet separated the belt from Yurakucho through Kyobashi and Nihonbashi—sea-level land called Edo-mae-shima.
Construction filled Hibiya Inlet and Edo-mae-shima. The inner citadel divides into two plateaus: from Kitanomaru to honmaru, and from fukiage to nishinomaru. Honmaru plateau was originally about 10 m elevation but was covered with up to 10 m of fill; ninomaru and sannomaru were also raised. The dry moat between honmaru and fukiage was made by filling the wide valley extending from Chidorigafuchi.
The honmaru keep platform remains, but until the 1657 Great Fire a magnificent "Kan'ei-era keep" stood 59 m including its base. The NPO "Society to Rebuild Edo Castle" (NPO Edo Castle Reconstruction) advances a movement to rebuild this wooden structure that pushed architectural limits. Imagining such a keep appearing before Palaceside Building makes the heart leap.