What was the primary building ingredient of a hang-t'u wall section?

Dirt is the primary building ingredient of a hang-t'u wall section. Hangtu, also known as Rammed earth, is an ancient construction method/technique used for building foundations, floors and walls. Dirt or clay-rich soil is mixed with gravel and sand. The damp mixture of these materials are compressed inside a temporary frame or "formwork" made of wood. The product can be a single wall or individual blocks.