Herma

A herma, commonly in English herm, is a sculpture with a head and sometimes a torso, above a tall squared pillar. Often a phallus was carved at the appropriate height. 
The form originated in Ancient Greece and was adopted by the Romans and revived in the Renaissance in the form of term figures. The name of the god Hermes comes from the word "herma", and the sculptures originally represented him.
The ancient Greeks and Romans were very superstitious, and the sculptures had an apotropiac function. They were placed at cross-roads and on the borders of lands as protection. 
In Athens, they were placed outside houses, temples and gymnasiums for good luck and to avert harmful or bad influences, like the evil eye. They would be adorned with garlands, wreaths, offerings and anointed with oil to obtain luck and protection.