Castles were built in Europe and the Middle East, with similar buildings developing separately in Japan in the 15th century. Castles were usually built from either wood or stone, and sometimes brick. Some castles started off as wooden and were then rebuilt in stone, which was more expensive and a stronger so that the castles could be bigger. They could be built on hills or low areas like the edge of towns or at river crossings. There is the widely held idea that castles were always built on high hills; while there are some castles which make dramatic use of the landscape and are highly visible, there were a lot of factors in choosing where to build castles and only a minority were on hills. For example, many castles were built along the Rhine River so they could stop people using the river without permission.