January 1st New Year's Day. Some say this is the only World Wide Holiday.
January is named for Janus God of 2 faces, the God that looks back and the God that looks forward.
The symbology of an Old Man representing the old year and a baby representing the New Year weaves seamlessly into the pagan Solstice and Stregheria rituals and celebrations, the ever changing, ever dying god. Janus encompasses both Lupercus the Wolf God who rules this time and Kern the Stag God whose rule begins at the Spring Equinox and ends at the Fall Equinox. Janus is the God who is present when the Child of Promise is born at Lupercus.
According to Wikipedia: "January is named after Janus (Ianuarius), the god of the doorway; the name has its beginnings in Roman mythology, coming from the Latin word for door (ianua) – January is the door to the year."
Again according to Wikipedia January has been the first month of the year for Romans since at least 153 BC, perhaps as far back as 450 BC or 713 BC depending on which account you prefer.
I prefer the 713 BC account which credits Numa Pompilius because I like his affliation with Egeria and Egeria's affliation with Lake Nemi. But I digress.
There is a great site that talks about how the Romans tracked days based on the Moon before they settled on a Solar Calendar. The excerpt below is taken from this site.
"January was named after Janus, a sky-god who was ancient even at the time of Rome’s founding. Ovid quoted Janus as saying "The ancients called me chaos, for a being from of old am I." After describing the world’s creation, he again quoted Janus: "It was then that I, till that time a mere ball, a shapeless lump, assumed the face and members of a god." A Lydian named Joannes identified Janus as a planet when he wrote: "Our own Philadelphia still preserves a trace of the ancient belief. On the first day of the month there goes in procession no less a personage than Janus himself, dressed up in a two-faced mask, and people call him Saturnus, identifying him with Kronos."
Early Romans believed that the beginning of each day, month and year were sacred to Janus. They thought he opened the gates of heaven at dawn to let out the morning, and that he closed them at dusk. This eventually led to his worship as the god of all doors, gates, and entrances."