Nerthus

The goddess Nerthus was a Germanic fertility goddess described by Tacitus. He describes a sacrifice to this goddess in a lake on what is sometimes interpreted as the island of Fyn, in Denmark.

In an island of the ocean there is a sacred grove and in it a carriage dedicated (to the goddess), covered with a vestment; only one priest is allowed to touch it. He feels the goddess' presence in her shrine, and follows with great veneration as she rides forth drawn by cows. Then come festive times for those whom she dignifies with her hospitality. They do not make war, they do not take up arms; all iron is put away; then, and only then, peace and quiet are known and loved, until she is satiated with the company of humans and the same priest returns the goddess to her sacred precinct. After this, the carriage and the vestment and, if you wish to believe it, the goddess herself, are washed in a secret lake. Slaves do this ministry and are then swallowed by the same lake: hence a mysterious terror and an ignorance full of reverence as to what that may be which men see only to die. (Germania, ch. 40)

The name is closely related to the name Njord, a god of the sea in Norse mythology. Her name may have survived in a few Scandinavian place names. However, due to the thousand years that passed between Tacitus's description and the Eddas, her role in Norse mythology can only be studied through speculation.

It has been suggested by Hilda R. Ellis Davidson in Gods and Myths of Northern Europe (1964) that there was possibly originally a male and female pair of deities, Njord and Nerthus, with Freyr later replacing Nerthus. She also makes the point that there were other male/female pairings of Norse gods of whom little is known but their names, e.g. Ullr and Ullin.

If so, she may have been the sister of Njord and the mother of his children, Freyr and Freya, who also had a sexual relationship according Loki in Lokasenna. This may be the reason why Snorri Sturluson wrote in the Ynglinga Saga that brother-sister marriages were common and accepted among the Vanir, but not among the Aesir.

If so, she was a logical counterpart of her brother Njord, in a society of fishermen and farmers, where she would have been associated with the harvest of the land, and her brother with the harvest of the sea.