Since the earliest known cultures of humanity, archeological findings show evidence that people worshiped a Mother Goddess. Many of these ancient goddesses are very elusive to modern study and research. Danu (also Dana or Anu), Mother Goddess of the Tuatha De Danann, is one such goddess that there are no surviving written legends of.
There is a possibility that Danu may have a connection to Saint Brigid of Kildare (also spelled Brighid), who is one of the patron saints of Ireland. The attributes of Danu, goddess of fertility and water, also include earth, agriculture, renewal and rebirth. Brigid of Kildare seems to have come forth just as Christianity edged out paganism and Druidism and became the prominent female to be worshiped in the early Celtic Christian Church. Saint Brigid is patron of Ireland, farmers, boatmen, sailors, mariners, water-men, as well as many other areas of Celtic life and needs.
In ancient times the Gaelic festival of Imbolc was celebrated half way between the Winter Solstice and Spring Equinox. It is a celebration to mark the end of the dark and dead and the beginning of renewal and rebirth. Imbolc is an ancient pagan festival in honor of the goddess Brighid, whose father is The Dagda, son of the goddess Danu -- some texts list Danu as the daughter of The Dagda since her traits are the same as Brighid's. Imbolc was adapted into a Christian holiday and called St. Brighid's Day.
The river Danube was known in ancient times as Danuvius, which is a word from a now extinct Celtic Gaulish language, which comes from the root word danu, which means river. It is believed by some scholars and mythologists that the river was named after the goddess Danu.
The Welsh mother goddess, Don, is also associated with the river Danube, Donau in Welsh. Like Danu, Don is only mentioned as the Mother Goddess and has no surviving written legends.
In County Kerry, Ireland are two mountains, side by side, in the shape of a woman's breasts. They are called the Paps of Anu. On the summit of each mountain stands a thirteen foot tall cairn. Ireland still remembers their ancient goddess Danu as the Mother of all.
Although the Tuatha de Danann are the most well-remembered and favorite inhabitants of ancient Ireland mythology, there is not much brought down in history about their Mother Goddess, Danu. Their name means the people of Danu and they are considered descendants of the goddess. The Dagda (The Good God) is the High King and Father of the Tuatha de Danann.
When the Tuatha de Danann were defeated by the Milesians, they retreated back to the north and eventually went to the Underworld to the realm of the faery. Since they lived and mingled with the faery folk they became like the Sidhe. Their Mother Goddess Danu is able to see between the two worlds, the realm of her people and and the realm they left behind.
Danu is the Mother Goddess of the Tuatha de Danann and the Sidhe, and is the Goddess of land and waters.