In the Archaic Triad of Roman gods, which one lacked a Greek counterpart?

In the Archaic Triad of Roman gods, Janus is the deity that lacked a direct Greek counterpart. The Archaic Triad consisted of Jupiter, Juno, and Minerva in later periods, but in the earliest times, it also included Janus, a uniquely Roman god who was not adopted from Greek mythology.

Janus is the god of beginnings, gates, transitions, time, duality, doorways, passages, frames, and endings. He is usually depicted as having two faces, since he looks to the future and to the past. The month of January (Januarius) is named after him, and his temple in the Roman Forum had doors that symbolized war and peace.

The concept of adopting and incorporating gods from other cultures was quite common in the ancient world. The Romans, in particular, were known for integrating deities from the pantheons of other peoples they came into contact with or conquered. This process is known as syncretism, where two or more religious beliefs are merged into a single new tradition.

While the Romans identified many of their own gods with Greek counterparts—such as Jupiter with Zeus, Juno with Hera, and Minerva with Athena—Janus remained a uniquely Roman god with no direct analogue in Greek mythology. Janus was considered an important deity in Roman religion and had a significant role in various religious rituals. The fact that Janus was depicted with two faces illustrates the Romans' understanding of transitions and the importance of looking to the past and future—a concept both practical and mystical. The doors to his temple in Rome would be open during times of war and closed during peace, reflecting his role as the divine intermediary between the Roman people and their gods, as well as a reflection of the state of the Republic and later the Empire.