Perpend stone

A perpend stone, perpend (parpen, parpend, perpin, and other spellings),^[1] through stone, bond stone, or tie stone is a stone that extends through an entire wall's width, from the outer to the inner wall. Such stones are especially used to lock two wall layers structurally together. Usually stone walls are built with two layers of stone, an inner and an outer layer, with the space between them sometimes filled with rubble.

The bond stones seen on the end of the right wall extend across the width of this tall, battered, dry-stone wall

The term perpend is also used to refer to a joint in brickwork also called a cross joint or, when extending through the entire wall, a transverse joint^[2] or perpend bond.^[3]

References

1. "Parpen, parpend" def. 1. Oxford English Dictionary Second Edition on CD-ROM (v. 4.0) © Oxford University Press 2009
2. Richard, H. W.. Bricklaying and Brickcutting,. London: Longmans, Green, and co., 1901. 4. Print.
3. Phillipps, Alfred Edward, ed.. Masonry construction; a guide to approved American practice in the selection of building stone, brick, cement, and other masonry materials, and in all branches of the art of masonry construction. Chicago: American school of correspondence, 1908. 64. Print.