A pounded earth embankment. It was made of layers of earth mixed with water, pounded down and allowed to harden. The wall had a flat top mabumi 馬踏, and widened towards the base. See diagram. The slope kōbai 勾配 of the sides varied: according to the Hōjō school, Hōjō-ryū 北条流, the wall should slope upwards at a 45 degree angle. This angle represented a safety standard by which to avoid the earth crumbling when the slopes were being built using form construction. The quality of the soil also made a difference: embankments constructed with black earth without pebbles and sand sometimes collapsed, unlike embankments of red loam that included large quantities of pebbles and sand. The standard measure for tatakidoi is a height of approximately 6 m (3 *ken 間), a flat top of width 4 m (2 ken) and both sloping sides 6 m wide, giving a total base width of about 16 m (8 ken).