As covered in earlier posts in this series, all ancient dwellings in Japan can be divided into one of two types: pit dwellings（竪穴住居, tateana juukyo), where a timber wall/roof structure was erected around an excavated pit which formed the below-ground floor of the dwelling; or the later raised-floor dwellings (高床住居, takayuka juukyo), with a timber floor structure elevated off the ground and supported between posts. In terms of their foundations, both of these types can (at least in their earliest forms) be categorised as ‘sunken post’ or ‘buried post’ (堀立て柱, horidate bashira) structures. As the name indicates, the timber structural posts (or inclined ridge-to-ground ‘rafters’) in these dwellings were set directly into the ground, usually to a depth of only 6-8 centimetres; their stability and that of the structure as a whole was obtained by connecting them above ground via a ridge beam, perimeter beams, purlins, and the like. The simplicity of this structural system allowed for the use of undressed, irregular, and crooked timbers, and didn’t require sophisticated tools or techniques. At the same time, these light, semi-permeable, and braced or triangulated structures demonstrated relatively good resistance against strong winds and snow loads.

An archaeological dig showing post-holes of *horidate-bashira* dwellings

The main disadvantage of this method is obvious: being in direct contact with the damp ground, the post bases were vulnerable to rot and insect attack, and soon decayed. Thus we see the appearance of foundation stones, either rough or dressed, placed half-buried in the ground, with posts set on top of them. At first, only ‘elite’ buildings like temples employed foundation stones, beginning in the Heian Period (794-1185); their adoption was extremely gradual, and horidate bashira survived in more humble minka and simple utility structures until the Edo Period (1603 - 1867) and even into the Meiji Period (1868 - 1912) in some regions. There were also many ‘transitional’ buildings that used a combination of posts on foundation stones and posts set directly into the ground.

*Horidate-bashira* on the left, posts on foundation stones on the right.

Diagram showing how a rotted-out *horidate-bashira* could be ‘upgraded’ to incorporate a foundation stone while retaining the healthy above-ground section of the post.

In the doma of the former Egawa Tarouzaemon residence, an early 17th century building perhaps better known for its wonderful lattice-like roof structure, there is an internal horidate bashira known as the iki-bashira or ‘living post,’ so called because it is said that the post was formed by simply cutting the upper trunk off a standing tree to the required height and dressing it in-situ, leaving the root system in place. Without excavation it is difficult to verify this story, but the earthen floor around the post displays a seemingly natural slope up to the ‘trunk’ of the post, hinting at the existence of a root structure beneath the surface.