are often monuments near castle structures or in their parks dedicated to either samurai or soldiers of the Imperial Army who died in war, such as the monument to the 18th Infantry Regiment near the ruins of Yoshida Castle (Toyohashi, Aichi). Castle grounds are often developed into parks for the benefit of the public, and planted with cherry blossom trees, plum blossom trees, and other flowering plants. Hirosaki Castle in Aomori Prefecture and Matsumae Castle in Hokkaido are both famous in their respective regions for their cherry blossom trees. The efforts of dedicated groups, as well as various agencies of the government has been to keep castles as relevant and visible in the lives of the Japanese people, to showcase them to visitors, and thus prevent the neglect of national heritage. Architecture and defenses Japanese castles were built in a variety of environments, but all were constructed within variations of a fairly well-defined architectural scheme. Yamajiro (山城), or "mountain castles" were the most common, and provided the best natural defenses. However, castles built on flat plains (平城, hirajiro) and those built on lowlands hills (平山城, hirayamajiro) were not uncommon, and a few very isolated castles were even built on small natural or artificial islands in lakes or the sea, or along the shore. The science of building and fortifying castles was known as chikujō-jutsu (). Walls and foundations Japanese castles were almost always built atop a hill or mound, and often an artificial mound would be created for this purpose (similar to European motte-and-bailey castles). This not only aided greatly in the defense of the castle, but also allowed it a greater view over the surrounding land, and made the castle look more impressive and intimidating. In some ways, the use of stone, and the development of the architectural style of the castle, was a natural step up from the wooden stockades of earlier centuries. The hills gave Japanese castles sloping walls, which many argue helped (incidentally) to defend them from Japan's frequent earthquakes. There is some disagreement among scholars as to whether or not these stone bases were easy to scale; some argue that the stones made easy hand- and footholds, while others retort that the bases were steep, and individual stones could be as large as high, making them difficult if not next to impossible to scale. Thus, a number of measures were invented to keep attackers off