Azuchi Castle
There were five main militaristic features of Azuchi Castle that differentiated it from earlier castle designs. Firstly, it was a massive structure, with the walls of the castle ranging from 5.5 to 6.5 meters in thickness. The second feature of Azuchi Castle is the predominant use of stone. The walls were constructed from huge granite stones fitted carefully together without the use of mortar. A third innovation of the Azuchi Castle was the high central tower, or "donjon". The tower allowed for increased visibility for the use of guns against an opposing force. Builder’s plans for the castle show the donjon to be 40 meters, with seven levels. Fourthly, Azuchi Castle had irregularly formed inner citadels. These inner citadels gave defenders ample defensive positions against intruders.