Anathyrosis

Anathyrosis is the technical term for how the ancients frequently dressed the joints of stone blocks. Since the blocks were set directly against each other without the use of mortar, the joint had to be exact. In order to reduce the amount of time required to form such a joint, the joining face of the stone was finished and smoothed only in a narrow contact band on the sides and top, while the interior of the face was recessed. The contact band looks somewhat like a doorframe, and the term - it was coined by the ancients - is allusive. "Thyra" (θύρα) is a Greek word for “door”, and so “door framing” is "anathyrosis." This technique was frequently employed in the construction of walls, including ashlar construction, and might be used between the drums of columns as well. Close examination of where this technique was applied to a stone can help to reveal its place within a structure or whether other stones were joined to it.

References

*Robertson, D. S. 1929. "Handbook of Greek and Roman Architecture". Cambridge: Cambridge University Press