Deity of the Greek Olympian pantheon, believed to be the messenger of the gods and a trickster who frequently travelled between divine and human realms. He is considered the patron deity of thieves, messengers, herdsmen, travellers, and merchants. In later Roman mythology, Hermes is equated with Mercury. The name Hermes likely derives from the ancient Greek herma, meaning a pile of stones that served to demarcate a boundary; it also refers to a sacred square-shaped stone carved with a bearded head and phallus, which was often the site of ritual sacrifice in ancient Greece. As Hermes developed into a classical Greek deity, he became associated with boundary-crossing and transgression. He is commonly shown carrying a winged staff entwined by two serpents known as a caduceus.