What do they call the stone head of a god surmounting a square stone pillar?

The stone head of a god surmounting a square stone pillar is commonly referred to as a "caryatid" or "herm." In ancient Greek and Roman architecture, such structures often served as decorative elements or markers of sacred significance. The term "herm" specifically refers to a pillar with a head, usually representing a deity or important figure, and was often used as a boundary marker or signpost.