Sangi-zumi

What sangi-zumi is

Sangi-zumi builds the outer corner of a stone wall by alternating the long and short faces of elongated stones from course to course. The Japanese name comes from the counting rods once used in mathematics.

Corners are where a stone wall fails first. Turning a long stone in a different direction at each course locks the two faces of the corner into one another, so that the angle holds.

It is used only at the corner, not across the wall. The west wall at the Hiraoka Residence in Tokushima Prefecture, from the early Meiji period, is described as a farmhouse wall facing the samurai quarter of a castle town, running in an L from the street towards the main house around the garden, 21.2 metres long, of split sandstone in six level courses, with the outer corner built this way and given a curved batter. Level courses across the face, interlocking stones at the corner.

The wall at Meisekiji in Ehime Prefecture is described the same way, roughly dressed stone in irregular courses with the corner built this way and curved.

Regularity as evidence of date

The technique grew more regular over time. The wall at the former Mori Residence in Hyogo Prefecture, built between the mid-Edo period and the Taisho era, is described as unworked stone along the middle and western parts of its north side, with the middle portion slightly later than the western and its corner more regularly built. Within one wall, the corner tells which part came first.

The curved batter recurs in these entries. Raising the face of a wall on a gentle curve rather than vertically demands accuracy at the corner, which is where the curve has to be carried through.

On site, stand at the corner and read the stones upward. Long and short faces alternating course by course identify the technique, and it must be read separately from how the rest of the wall is laid.