There is a room a hundred and forty metres long with no columns in it. The reeling hall at the Tomioka Silk Mill runs to about that length, and the roof is carried on trusses so that the floor beneath is clear from end to end. The absence of columns is not architectural ambition: it exists because the reeling machines had to stand in one continuous line, and the mill was equipped at its founding with three hundred metal reeling basins imported from France.

The east and west cocoon warehouses are each about a hundred and four metres long, with the cocoons stored on the upper floor. All of it is built as timber framing infilled with brick, a construction chosen because it could be put up quickly by carpenters who had never worked in brick before. The reeling hall and the two warehouses were designated national treasures in December 2014. Along the street outside are shops and storehouses, the Jōshin railway runs to Takasaki, and the town has hospitals and shopping gathered in its centre.

A factory building is dictated by how its machines have to be arranged. Three hundred basins in a row require a very long room; a very long room cannot have columns interrupting the line; and the only way to roof it without them is a truss. Everything about this building follows from the equipment that had to stand inside it, in that order, and none of it was decided the other way round. The figure of a hundred and forty metres is simply the number of machines, translated into architecture by people solving a practical problem.