The Roman god who protected boundary markers and was honored at the Terminalia festival was Terminus.
Terminus embodied the sacred boundary itself, especially the stone or post separating neighboring properties. Romans treated these markers as more than practical surveying tools: disturbing one could violate divine law and provoke serious punishment. The god’s name comes from the Latin term for a boundary marker.
The Terminalia took place on February 23. Neighboring landowners decorated opposite sides of a boundary stone with garlands, built a small altar, and offered grain, honeycombs, wine, and sometimes a lamb or suckling pig. These rites renewed the marker’s sanctity and encouraged peaceful relations between properties.
A famous stone associated with Terminus stood within the Temple of Jupiter Optimus Maximus on Rome’s Capitoline Hill. According to tradition, it was not moved when the temple was built, and an opening in the roof allowed sacrifices to be made under the open sky. This connection sometimes led Romans to call the deity Jupiter Terminalis, but Terminus remains the canonical answer to the question.