The main tower of Osaka Castle is situated on a plot of land roughly one square kilometer. It is built on two raised platforms of landfill supported by sheer walls of cut rock, using a technique called Burdock piling, each overlooking a moat. The central castle building is five stories on the outside and eight stories on the inside, and built atop a tall stone foundation to protect its occupants from attackers. The Castle grounds, which cover approximately 60,000 square meters (15 acres)[2] contain thirteen structures which have been designated as Important Cultural Assets by the Japanese government.