In Germania, Tacitus records that the remote Suebi tribes were united by their veneration of the goddess at his time of writing and maintained a sacred grove on an (unspecified) island and that a holy cart rests there draped with cloth, which only a priest may touch. The priests feel her presence by the cart, and, with deep reverence, attend her cart, which is drawn by heifers. Everywhere the goddess then deigns to visit, she is met with celebration, hospitality, and peace. All iron objects are locked away, and no one will leave for war. When the goddess has had her fill she is returned to her temple by the priests. Tacitus adds that the goddess, the cart, and the cloth are then washed by slaves in a secluded lake. The slaves are then drowned.
The name Nerthus is generally held to be a Latinized form of Proto-Germanic *Nerþuz, a direct precursor to the Old Norse deity name Njörðr. While scholars have noted numerous parallels between the descriptions of the two figures, Njörðr is attested as a male deity. Various scholarly theories exist regarding the goddess and her potential later traces amongst the Germanic peoples, including that the figure may be identical to the unnamed sister-wife of Njörðr mentioned in two Old Norse sources.
Nerthus is often identified with the van Njörðr who is attested in various 13th century Old Norse works and in numerous Scandinavian place names. The connection between the two is due to the linguistic relationship between Njörðr and the reconstructed Proto-Germanic *Nerþuz, Nerthus being the feminine, Latinized form of what Njörðr would have looked like around the first century. This has led to theories about the relation of the two, including that Njörðr may have once been a hermaphroditic deity or that the name may indicate the otherwise forgotten sister-wife in a divine brother-sister pair like the Vanir deities Freyja and Freyr.
While developments in historical linguistics ultimately allowed for the identification of Nerthus with Njörðr, various other readings of the name were in currency prior to the acceptance of this identification, most commonly the form Hertha. This form was proposed as an attempt to mirror the Old Norse goddess name Jörð 'earth'. Writing on this topic in 1912, Raymond Wilson Chambers says "strange has been the history of this goddess Nerthus in modern times. Sixteenth century scholars found irresistible the temptation to emend the name of 'Mother Earth' into Herthum, which nineteenth century scholars further improved into Hertham, Ertham. For many years this false goddess drove out the rightful deity from the fortieth chapter of the Germania". Up until its superseding, the name Hertha had some influence. For example, Hertha and Herthasee (see "location" section below) play major roles in German novelist Theodor Fontane's 1896 novel Effi Briest.
In chapter 40 of his Germania, Roman historian Tacitus, discussing the Suebian tribes of Germania, writes that beside the populous Semnones and warlike Langobardi there are seven remoter Suebian tribes; the Reudigni, Aviones, Anglii, Varini, Eudoses, Suarines, and Nuitones. The seven tribes are surrounded by rivers and forests and, according to Tacitus, there is nothing particularly worthy of comment about them as individuals, yet they are particularly distinguished in that they all worship the goddess Nerthus, and provides an account of veneration of the goddess among the groups. The chapter reads as follows:
- Contra Langobardos paucitas nobilitat: plurimis ac valentissimis nationibus cincti non per obsequium, sed proeliis ac periclitando tuti sunt. Reudigni deinde et Aviones et Anglii et Varini et Eudoses et Suardones et Nuithones fluminibus aut silvis muniuntur. Nec quicquam notabile in singulis, nisi quod in commune Nerthum, id est Terram matrem, colunt eamque intervenire rebus hominum, invehi populis arbitrantur. Est in insula Oceani castum nemus, dicatumque in eo vehiculum, veste contectum; attingere uni sacerdoti concessum. Is adesse penetrali deam intellegit vectamque bubus feminis multa cum veneratione prosequitur. Laeti tunc dies, festa loca, quaecumque adventu hospitioque dignatur. Non bella ineunt, non arma sumunt; clausum omne ferrum; pax et quies tunc tantum nota, tunc tantum amata, donec idem sacerdos satiatam conversatione mortalium deam templo reddat. Mox vehiculum et vestes et, si credere velis, numen ipsum secreto lacu abluitur. Servi ministrant, quos statim idem lacus haurit. Arcanus hinc terror sanctaque ignorantia, quid sit illud, quod tantum perituri vident.
A. R. Birley translation:
- By contrast, the Langobardi are distinguished by being few in number. Surrounded by many mighty peoples they have protected themselves not by submissiveness but by battle and boldness. Next to them come the Ruedigni, Aviones, Anglii, Varini, Eudoses, Suarines, and Huitones, protected by river and forests. There is nothing especially noteworthy about these states individually, but they are distinguished by a common worship of Nerthus, that is, Mother Earth, and believes that she intervenes in human affairs and rides through their peoples. There is a sacred grove on an island in the Ocean, in which there is a consecrated chariot, draped with cloth, where the priest alone may touch. He perceives the presence of the goddess in the innermost shrine and with great reverence escorts her in her chariot, which is drawn by female cattle. There are days of rejoicing then and the countryside celebrates the festival, wherever she designs to visit and to accept hospitality. No one goes to war, no one takes up arms, all objects of iron are locked away, then and only then do they experience peace and quiet, only then do they prize them, until the goddess has had her fill of human society and the priest brings her back to her temple. Afterwards the chariot, the cloth, and, if one may believe it, the deity herself are washed in a hidden lake. The slaves who perform this office are immediately swallowed up in the same lake. Hence arises dread of the mysterious, and piety, which keeps them ignorant of what only those about to perish may see.
J. B. Rives translation:
- The Langobardi, by contrast, are distinguished by the fewness of their numbers. Ringed round as they are by many mighty peoples, they find safety not in obsequiousness but in battle and its perils. After them come the Reudingi, Aviones, Anglii, Varini, Eudoses, Suarini and Nuitones, behind their ramparts of rivers and woods. There is nothing noteworthy about these peoples individually, but they are distinguished by a common worship of Nerthus, or Mother Earth. They believe that she interests herself in human affairs and rides among their peoples. In an island of the Ocean stands a sacred grove, and in the grove a consecrated cart, draped with cloth, which none but the priest may touch. The priest perceives the presence of the goddess in this holy of holies and attends her, in deepest reverence, as her cart is drawn by heifers. Then follow days of rejoicing and merry-making in every place that she designs to visit and be entertained. No one goes to war, no one takes up arms; every object of iron is locked away; then, and only then, are peace and quiet known and loved, until the priest again restores the goddess to her temple, when she has had her fill of human company. After that the cart, the cloth and, if you care to believe it, the goddess herself are washed in clean in a secluded lake. This service is performed by slaves who are immediately afterwards drowned in the lake. Thus mystery begets terror and pious reluctance to ask what the sight can be that only those doomed to die may see.
A number of theories have been proposed regarding the figure of Nerthus, including the location of the events described, relations to other known deities and her role amongst the Germanic tribes.
A number of scholars have proposed a potential location of Tacitus's account of Nerthus as on the island of Zealand in Denmark. The reasoning behind this notion is the linking of the name Nerthus with the medieval place name Niartharum (modern Nærum) located on Zealand. Further justification is given in that Lejre, the seat of the ancient kings of Denmark, is also located on Zealand. Nerthus is then commonly compared to the goddess Gefjon, who is said to have plowed the island of Zealand from Sweden in the Prose Edda book Gylfaginning and in Lejre wed the legendary Danish king Skjöldr.
Chambers notes that the mistaken name Hertha (see Interpretations of name above) led to the hydronym Herthasee, a lake on the German island of Rügen, which antiquarians proposed as a potential location of the Nerthus site described in Tacitus. However, along with the rejection of the reading Hertha, the location is now no longer considered as a potential site.
Nerthus typically is identified as a Vanir goddess. Her wagon tour has been likened to several archeological wagon finds and legends of deities parading in wagons. Terry Gunnell and many others have noted various archaeological finds of ritual wagons in Denmark dating from 200 AD and the Bronze Age. Such a ceremonial wagon, incapable of making turns, was discovered in the Oseberg ship find. Two of the most famous literary examples occur in the Icelandic family sagas. The Vanir god Freyr is said to ride in a wagon annually through the country accompanied by a priestess to bless the fields, according to a late story titled Hauks þáttr hábrókar in the 14th century Flateyjarbók manuscript. In the same source, King Eric of Sweden is said to consult a god named Lýtir, whose wagon was brought to his hall in order to perform a divination ceremony.
Hilda Davidson draws a parallel between these incidents and Tacitus's account of Nerthus, suggesting that in addition a neck-ring-wearing female figure "kneeling as if to drive a chariot" also dates from the Bronze Age. Davidson says that the evidence suggests that similar customs as detailed in Tacitus's account continued to exist during the close of the pagan period through worship of the Vanir.