At first sight it may seem strange that Mercury and Odin were regarded as identical. We are wont to conceive Hermes (Mercury) as the Greek sculptors represented him, the ideal of beauty and elastic youth, while we imagine Odin as having a contemplative, mysterious look. And while Odin in the Teutonic mythology is the father and ruler of the gods, Mercury in the Roman has, of course, as the son of Zeus, a high rank, but his dignity does not exempt him from being the very busy messenger of the gods of Olympus. But neither Greeks nor Romans nor Teutons attached much importance to such circumstances in the specimens we have of their comparative mythology. The Romans knew that the same god among the same people might be represented differently, and that the local traditions also sometimes differed in regard to the kinship and rank of a divinity. They therefore paid more attention to what Tacitus calls vis numinis—that is, the significance of the divinity as a symbol of nature, or its relation to the affairs of the community and to human culture. Mercury was the symbol of wisdom and intelligence; so was Odin. Mercury was the god of eloquence; Odin likewise. Mercury had introduced poetry and song among men; Odin also. Mercury had taught men the art of writing; Odin had given them the runes. Mercury did not hesitate to apply cunning when it was needed to secure him possession of something that he desired; nor was Odin particularly scrupulous in regard to the means. Mercury, with wings on his hat and on his heels, flew over the world, and often appeared as a traveller among men; Odin, the ruler of the wind, did the same. Mercury was the god of martial games, and still he was not really the war-god; Odin also was the chief of martial games and combats, but the war-god's occupation he had left to Tyr. In all important respects Mercury and Odin, therefore, resembled each other.
To the scholars this must have been an additional proof that this, in their eyes, historical chief, whom the Romans called Mercury and the Teutons Odin, had been one and the same human person, who had lived in a distant past, and had alike induced Greeks, Romans, and Goths to worship him as a god. To get additional and more reliable information in regard to this Odin-Mercury than what the Teutonic heathen traditions could impart, it was only necessary to study and interpret correctly what Roman history had to say about Mercury.
As is known, some mysterious documents called the Sibylline books were preserved in Jupiter's temple, on the Capitoline Hill, in Rome. The Roman State was the possessor, and kept the strictest watch over them, so that their contents remained a secret to all excepting those whose position entitled them to read them. A college of priests, men in high standing, were appointed to guard them and to consult them when circumstances demanded it. The common opinion that the Roman State consulted them for information in regard to the future is incorrect. They were consulted only to find out by what ceremonies of penance and propitiation the wrath of the higher powers might be averted at times when Rome was in trouble, or when prodigies of one kind or another had excited the people and caused fears of impending misfortune. Then the Sibylline books were produced by the properly-appointed persons, and in some line or passage they found which divinity was angry and ought to be propitiated. This done, they published their interpretation of the passage, but did not make known the words or phrases of the passage, for the text of the Sibylline books must not be known to the public. The books were written in the Greek tongue.
The story telling how these books came into the possession of the Roman State through a woman who sold them to Tarquin—according to one version Tarquin the Elder, according to another Tarquin the Younger—is found in Roman authors who were well known and read throughout the whole middle age. The woman was a Sibylla, according to Varro the Erythreian, so called from a Greek city in Asia Minor; according to Virgil the Cumæan, a prophetess from Cumæ in southern Italy. Both versions could easily be harmonised, for Cumæ was a Greek colony from Asia Minor; and we read in Servius' commentaries on Virgil's poems that the Erythreian Sibylla was by many regarded as identical with the Cumæan. From Asia Minor she was supposed to have come to Cumæ.
In western Europe the people of the middle age claimed that there were twelve Sibyllas: the Persian, the Libyan, the Delphian, the Cimmerinean, the Erythreian, the Samian, the Cumæan, the Hellespontian or Trojan, the Phrygian and Tiburtinian, and also the Sibylla Europa and the Sibylla Agrippa. Authorities for the first ten of these were the Church father Lactantius and the West Gothic historian Isodorus of Sevilla. The last two, Europa and Agrippa, were simply added in order to make the number of Sibyllas equal to that of the prophets and the apostles.
But the scholars of the middle ages also knew from Servius that the Cumæan Sibylla was, in fact, the same as the Erythreian; and from the Church father Lactantius, who was extensively read in the middle ages, they also learned that the Erythreian was identical with the Trojan. Thanks to Lactantius, they also thought they could determine precisely where the Trojan Sibylla was born. Her birthplace was the town Marpessus, near the Trojan Mount Ida. From the same Church father they learned that the real contents of the Sibylline books had consisted of narrations concerning Trojan events, of lives of the Trojan kings, &c., and also of prophecies concerning the fall of Troy and other coming events, and that the poet Homer in his works was a mere plagiator, who had found a copy of the books of the Sibylla, had recast and falsified it, and published it in his own name in the form of heroic poems concerning Troy.
This seemed to establish the fact that those books, which the woman from Cumæ had sold to the Roman king Tarquin, were written by a Sibylla who was born in the Trojan country, and that the books which Trojan bought off her contained accounts and prophecies—accounts especially in regard to the Trojan chiefs and heroes afterwards glorified in Homer's poems. As the Romans came from Troy, these chiefs and heroes were their ancestors, and in this capacity they were entitled to the worship which the Romans considered due to the souls of their forefathers. From a Christian standpoint this was of course idolatry; and as the Sibyllas were believed to have made predictions even in regard to Christ, it might seem improper for them to promote in this manner the cause of idolatry. But Lactantius gave a satisfactory explanation of this matter. The Sibylla, he said, had certainly prophesied truthfully in regard to Christ; but this she did by divine compulsion and in moments of divine inspiration. By birth and in her sympathies she was a heathen, and when under the spell of her genuine inspirations, she proclaimed heathen and idolatrous doctrines.
In our critical century all this may seem like mere fancies. But careful examinations have shown that an historical kernel is not wanting in these representations. And the historical fact which lies back of all this is that the Sibylline books which were preserved in Rome actually were written in Asia Minor in the ancient Trojan territory; or, in other words, that the oldest known collection of so-called Sibylline oracles was made in Marpessus, near the Trojan mountain Ida, in the time of Solon. From Marpessus the collection came to the neighbouring city Gergis, and was preserved in the Apollo temple there; from Gergis it came to Cumæ, and from Cumæ to Rome in the time of the kings. How it came there is not known. The story about the Cumæan woman and Tarquin is an invention, and occurs in various forms. It is also demonstrably an invention that the Sibylline books in Rome contained accounts of the heroes in the Trojan war. On the other hand, it is absolutely certain that they referred to gods and to a worship which in the main were unknown to the Romans before the Sibylline books were introduced there, and that to these books must chiefly be attributed the remarkable change which took place in Roman mythology during the republican centuries. The Roman mythology, which from the beginning had but few gods of clear identity with the Greek, was especially during this epoch enlarged, and received gods and goddesses who were worshipped in Greece and in the Greek and Hellenised part of Asia Minor where the Sibylline books originated. The way this happened was that whenever the Romans in trouble or distress consulted the Sibylline books they received the answer that this or that Greek-Asiatic god or goddess was angry and must be propitiated. In connection with the propitiation ceremonies the god or goddess was received in the Roman pantheon, and sooner or later a temple was built to him; and thus it did not take long before the Romans appropriated the myths that were current in Greece concerning these borrowed divinities. This explains why the Roman mythology, which in its oldest sources is so original and so unlike the Greek, in the golden period of Roman literature comes to us in an almost wholly Greek attire; this explains why Roman and Greek mythology at that time might be regarded as almost identical. Nevertheless the Romans were able even in the later period of antiquity to discriminate