In Greek mythology, which day of the month was sacred to Hermes?

In Greek mythology, the fourth day of the month was sacred to Hermes.

The association comes from the Homeric Hymn to Hermes, which presents the god as being born on the fourth day of the lunar month. Ancient Greek religious calendars often gave particular days to deities, heroes, or ritual observances, so the date carried religious meaning beyond simply marking time.

The fourth day also fits Hermes’ mythic identity as a god connected with beginnings, movement, messages, trade, and clever invention. The Homeric Hymn describes his precocious activity immediately after birth, including his theft of Apollo’s cattle and the creation of the lyre.

This fact is separate from the Hermaia, a festival held in Hermes’ honor. The festival was associated especially with athletic activity and youth, while the fourth day refers to the recurring calendar date sacred to him.