The door of history turns on small hinges, and so do people’s lives. –Thomas S. Monson
On this day, the pontiffs would announce the number of days until the next month at the Curia Calabra; in addition, debtors had to pay off their debts on this day. These debts were inscribed in the kalendaria, effectively an accounting book.
Cardea is the Roman Goddess of the Door Hinge, who protects the family and children of the house and keeps evil spirits from crossing the threshold. Her name comes from the Latin word cardo, which means "hinge" and which also encompasses the wider symbolism of the pole or axis around which the earth spins. She is therefore a Goddess of the Center as well as the change that emanates out from that center. The word cardo was also used by the Romans to refer to the north-south axis on which a new city was founded (the east-west line being the decumanus), and from this we get our word cardinal, meaning fundamental or principal, especially regarding the directions.
Cardea has close ties with the ancient Roman God Janus, God of Beginnings and Endings, who also watched over doorways, and was depicted as having two faces to see both past and future (our month January, the first month of the year, is still named for Him). The tales say that Cardea and Janus were lovers; and to reward Her for sleeping with Him, or perhaps from love, He gave Her the door-hinge as Her emblem, and the power to prevent evil spirits from passing through doors. Because She could keep bad spirits out of the house, Cardea was worshipped as the protector of children, for it was believed (or at least the children believed) that at night witches transformed themselves into screech-owls and flew in the windows of the house to suck the blood of unwary children. (The Latin words striga, "witch, hag, vampire", and strix, "screech owl, vampire" are clearly related.)
The legends say that Cardea protected these children with hawthorn (also known as whitethorn), by hanging a small branch of it over the child's window or in the baby's cradle.