Used by Sumerians and other Mesopotamian cultures beginning in the third millennium BC, clay nails, also referred to as dedication or foundation pegs, cones, or nails, were cone-shaped nails made of clay, inscribed with cuneiform, baked, and stuck into the mud-brick walls to serve as evidence that the temple or building was the divine property of the god to whom it was dedicated.
Source: Clay nail – Wikipedia
Tim B.
https://en.wikipedia.org/wiki/Funerary_cone