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. Hawthorn is considered a sacred plant in legend and is famous in folklore for its magical powers of protection. Ovid confuses Cardea with Carna, the protective Goddess of the internal organs, but relates a legend in which the Goddess banished vampires from a young boy's room, healing his sickness and making him well. After purifying the doorposts and threshold with a sprig of arbutus (of which the strawberry tree is one species), a sow was sacrificed as a symbolic replacement for the child. In the last part of the ritual a hawthorn branch was then hung in the window. This child was Procas, a young prince of Alba Longa, who in due time would be the grandfather of Romulus and Remus, the legendary founders of Rome. Alba Longa was a city of the Latins, about 20 miles from Rome, located on Albanus Mountain overlooking Albanus Lake, and is said to have been named for the white sow possessed by Aeneas. All these place-names have as their root the Latin word for "white", and the white sow recalls the sacrifice in the legend.

Cardea seems to have survived into the 19th century in the local folklore of Tuscany, as a witch called Carradora. A strikingly similar story is told of her in which she cures a sick baby. She drives out the blood-sucking witches who are causing the illness with twigs of arbutus and hawthorn wrapped in red cloth, which are hung in doorways and windows.

Also called: Carda, Carna (erroneously, but they are still confused), Crane (said by Ovid to be an older form of Carna), Clererca (said to be Her Italian name).