Janus am I; oldest of potentates;
Forward I look, and backward, and below
I count, as god of avenues and gates,
The years that through my portals come and go.
From: The Poet’s Calendar by Longfellow
Janus is the deity who presides over doorways (januae) and archways (jani), and, by extension, beginnings and endings. He is invoked at the beginning of every ritual because, as the gate-keeper of Olympus, he permitted the prayers of mortals to enter and to be received by the immortal gods.