Based on the inscription, the altar appears to have been dedicated by a soldier named Gaius Cassius Flavianus, who may have been in command of the Roman military base in Inveresk, Scotland. In A.D. 142, the fort at Inveresk was established along the Antonine Wall, where Roman soldiers were sent to protect the northernmost frontier of the Roman Empire.

According to National Museums Scotland, which recently acquired the Altar to Sol along with a second altar that honors the god Mithras, these monuments would have been focal points for worshippers participating in secret religious ceremonies. The mythical Mithras was born from a rock and was often depicted slaying a bull. Sol played an important role in the Mithras cult and was sometimes equated with Mithras.

Temples to Mithras, called Mithraea, were always situated underground, and only men were allowed to join the mysterious cult, which purported to celebrate the triumph of light over darkness and goodness over evil.

"In the dark of the temple, you would see the rays and the eyes of the sun god glaring at you," Fraser Hunter, curator of Iron Age and Roman archaeology at National Museums Scotland, explained in a video. The altars to Sol and Mithras are unique in Scotland and point to the beliefs of soldiers stationed along the Antonine Wall. Mithras and Sol gave soldiers "a sense that there was a purpose to the world and that there was a life after death," Hunter said.

The rare carved altars will be on display at National Museums Scotland starting Nov. 14.

For more stunning archaeological discoveries, check out our Astonishing Artifacts archives.

Kristina Killgrove is a staff writer at Live Science with a focus on archaeology and paleoanthropology news. Her articles have also appeared in venues such as Forbes, Smithsonian, and Mental Floss. Kristina holds a Ph.D. in biological anthropology and an M.A. in classical archaeology from the University of North Carolina, as well as a B.A. in Latin from the University of Virginia, and she was formerly a university professor and researcher. She has received awards from the Society for American Archaeology and the American Anthropological Association for her science writing.