On Ponte Fabricio, the oldest bridge in Rome, sit the two best known hermai of Janus. (A 3rd was repurposed for Belli’s memorial in Trastevere.) Hermai in ancient Greek are stone pillars used to mark boundaries, upon which gods’ heads were usually carved, and which one touched when passing by for good luck. (One god in particular, more common on hermai for being associated with travel, movement, messages, etc., was eventually simply called “Hermes”.)
Enough ancient Greece, on to Rome. Janus was the god of liminal spaces . . physical passages, such as doors, gates, and bridges, as well as all abstract passages, such as beginnings, ends, transitions, and change. You get one guess where the name for the month of January comes from . . . or even “janitor”, the caretaker of hallways, custodian of the keys to all doors.
Janus is always depicted with two heads facing in opposite directions. A great motif! What better way to symbolize transitions, being neither here nor there, past nor future, but by depicting that god as literally astride both.
Truth be told the special four-faced hermai of Janus on Ponte Fabricio are in terrible shape. While not much to look at, what is interesting is that they are still being touched for good luck . . today, like 2000 years ago, and no doubt tomorrow as well. Janus would approve!