Commonly considered to be the seat of the ancient Saxon religion located near Heresburg (now Obermarsberg) in Northern Germany, the first reference to Irminsul appeared in the Annales Regni Francorum or Royal Frankish Annals (772 AD). During the Saxon wars, Charlemagne repeatedly ordered the idol’s destruction. Rudolf of Fulda (865 AD) describes it in his De Miraculis Sancti Alexandri ("The Miracles of Saint Alexander"), chapter III, as a great wooden pillar erected and worshipped under the open sky. In some sources, this pillar is personified.

Widukind of Corvey in Deeds of the Saxons (c. 970) describes such an Irminsul erected to celebrate the Saxon's victory over the Thuringians in 531. He says the Saxons set up an altar to their god of victory, identified as Hirmin or Hermes (Mercury), whom they depicted as a wooden column. In 1605, four decades before the Codex Regius came to light, the Irminsul was directly identified with both Mercury and Odin. Richard Verstegan, in his Restitution of Decayed Intelligence in Antiquities, writes:

“Whereas Tacitus saith, that of all the Gods the Germans especially honored Mercury find upon certaine dayes offered men unto him in sacrifice, this Idol Ermensewl (Irminsul) is taken to be the same that the Romans interpreted for Mercury, though some others have interpreted him for Mars, and Woden with less reasone for Mercury; for that he was held of the Saxons for their God of war, as Mercury among the Romans never was. And in all likelihood of truth, the Romans for some property which the Germans ascribed to their Idols, might well for the like property ascribed by them unto theirs, take them to be the very same Idols, albeit they were of the Germans called by other names, and made in other manner. And so in like sort hath Thor been of some interpreted for Iupiter, for that among his other marvels he made, and caused, thunder, and was chiefly honoured upon the same day whereon the Romans honoured their Iupiter. Friga is also interpreted for Venus because among other her qualities she was a furtherer of friendship, and that on the very day of her chiefe celebration, the Romans chiefly honoured their amiable Venus.”

A much clearer parallel can be seen in an even earlier source, briefly mentioned before, which links the Germanic Mercury to a goddess designated as Vrowe Here (Frau Here), said to be worshiped together with him by the ancient Saxons.  As such it is worth quoting at length. Penned by Gobelin Person (Gobelinus Persona, 1358-1421), a prominent historian and church reformer from the bishopric of Paderborn in North Rhine-Westphalia, his master work Cosmidromius, completed in 1418, remains one of the most important historical works of the fifteenth century. In chapter 38, composed some time before 1406, speaking of local history and superstition, he writes:

"Charles the Great in the year of our Lord 769, took hold of the reign in the kingdom of the Franks and ruled for forty-six years; of course, three years together with his brother Carlomann and the remainder of the years ruled alone. In the second year of his reign, the General Assembly of Worms convened to decide upon the approach to the Saxon War, and they, without delay, advanced altogether with swords and fire to plunder the castle of Eresburgh, which presently is called Mount Mars in the Latin tongue, and seized the idol which the Saxons call Irminsuel, destroyed it and then took it back all the way up to the Weser River, and withdrew with twelve Saxon hostages. Understand that this idol Irminsuel is Mercury or what the Greeks call Hermes 
...They consecrate the idol or statue in the aforementioned place to this god, because Irminsuel is a statue of he who is called Hermes. And because in this aforementioned place all men in the district assemble in order to sacrifice to the idol out of reverence and devote themselves to it, that place is called Eresburgh, the Mountain of Reverence. Actually Juno, who, in the writings of the Greeks, is called Hera, was worshiped in the same place before Hermes or perhaps at the same time, thereupon they call that place Heresbergh, which is clearly the Mountain of Hera or Juno, and afterwards, once they occupied and fortified that place, called it Heresburgh, the Castle of Hera. Moreover, this Hera was worshiped by the Saxons, which can be seen by the fact that certain of the common people recite what they themselves have heard from antiquity, just as I myself have heard, that between the festival of the Birth of Christ and the holiday of the Epiphany of the Lord, Mistress Hera flies through the air, because the pagans assign the air to Juno. And because, whenever they call upon Juno as Ceres and depict her with bells and wings, the common people call her vrowe here (Frau Here), or corrupt the name Vor Here de Vlughet [of Flight], and believe that she brings abundance at that time." 

The significance of this remarkable passage cannot be overstated. Written nearly two decades before the re-discovery of Tacitius’ Germania in 1425, it clearly identifies a local Saxon god with Mercury, which Germania and a handful of other sources also identify as Odin (see further). The author expressly speaks of local belief, recording what “the common people” said they “themselves have heard from antiquity [or the elders], just as I myself have heard.”  Although he travelled widely throughout Italy in the company of Pope Urban VI before being ordained in 1386, Gobelin Person was a native of Paderborn, Germany who was born, bred, and ultimately buried in the vicinity. Although deeply learned, he was in a position to both know and understand local legend. Remarkably, he not only identifies the local Saxon goddess known as Frau Here (Vrowe Here) with the Greek goddess Hera, the Queen of the Classical pantheon, but also identifies her with Ceres, the Roman goddess of agriculture, demonstrating that the identification was based on more than just a superficial similarity between the names Here and Hera. Among the Saxons, Vrowe Here [Frau Here] is thus the Queen of Heaven and Mother Earth at the same time. Drawing on ancient local tradition which he himself had heard, he says that the common folk believe she flies through the air between Christmas and New Year’s Day bringing abundance, adding the unique details that she was depicted with bells and wings.  These last two details directly correspond to what we know of Frau Percht, whose followers, the Perchten, frequently sound bells [See Chapter IV: The Frau Holle Legends]. The same is said of the followers of Freyr, lord of harvests. In the sixth book of his Danish history, Saxo says that the hero Starkad went to Old Uppsala where he saw the Sons of Frey perform on stage at the time of the sacrifices: 

"He went to the land of the Swedes, where he lived at leisure for seven years’ space with the sons of Frey ... he was stationed at Uppsala at the time of the sacrifices, he was disgusted by the effeminate gestures and the clapping of mimes on the stage, and by the unmanly clatter of bells. Hence it is clear, how far he kept his soul from lasciviousness, not even enduring to look upon it," (Oliver Elton translation). 

Saxo describes the shows from his Christian perspective as lascivious, fitting for a god of fertility. At Uppsala, Freyr was called Fricco and depicted with an immense phallus; he presided over marriages. The name Fricco directly connects him to Frick, Frikka, Frekka, which as we have seen are alternate names of Frau Holle, and to Frigga, the beloved wife of Odin. That she has wings can be confirmed by images in the iconography and mythology of the region which is well-acquainted with prophetic goddesses in the form of birds. According to Skaldskaparmál 18, Frigg, like Freyja, owns a falcon guise which Loki borrows. Remarkably, Gobelin couples the veneration of this “Vrowe Here” and her local sanctuary with that of the Classical Mercury, who is widely recognized as Odin from other Latin sources. In addition, he precisely pinpoints the time of her flight as taking place between the Feasts of the Nativity and the Epiphany, corresponding to the Twelves, the time of the annual progress of Frau Holle, as well as the ride of Wild Hunt in Northern European tradition, when Odin and his wife flew through the air visiting homes —all this according to local oral legends concerning the old Saxons, which the author himself had heard in the latter part of the fourteenth century as a native of Paderborn, beginning with the Christian invasion of Saxon territory and the destruction of their sacred pillar, the Irminsul, which Gobelin identifies as an idol of Mercury at Eresburg [Heresburgh], now the city of Obermarsberg, south of Paderborn some 650 years earlier. 

Excerpt from Odin's Wife: Mother Earth in Germanic Mythology
by William P. Reaves (c) 2018

https://norroena.org/product/odins-wife-mother-earth-in-germanic-mythology/