A horse arena requires tons of base and top material. These heavy materials cost a lot to move around, and therefore it is not economical to ship these kinds of materials any distance at all. Therefore when building a horse arena, the local materials need to be used. Each locality has materials available that are different in their properties. An expert arena-builder needs to examine the locally available materials and make decisions about which ones to use and how to adjust the rest of the structure to adapt to the unique properties of the local materials.