Taranis:

1.

We'll start with the only literary primary sources on file for Taranis: the Roman poet Lucian!

Lucian's Pharsalia:

Lucian is our first source about Taranis. He isn't noted as a great God to worship, but as this is one of our few literary sources, we have to run with it:

"...and those Gauls who propitiate with human sacrifices the merciless gods Teutas, Esus and Taranis - at whose alters the visitany shudders because they are as awe-inspiring as those of the Scythian Diana."

Lucan, Pharsalia I, 422-465 ( http://www.kernunnos.com/deities/Taranis.shtml)

Here's another translation, with different line numbers:

     Ligurian tribes, now shorn, in ancient days
     First of the long-haired nations, on whose necks
     Once flowed the auburn locks in pride supreme;
     And those who pacify with blood accursed
     Savage Teutates, Hesus' horrid shrines,
500  And Taranis' altars cruel as were those
     Loved by Diana (18), goddess of the north;
     All these now rest in peace.  And you, ye Bards,
     Whose martial lays send down to distant times
     The fame of valorous deeds in battle done,
     Pour forth in safety more abundant song.
     While you, ye Druids (19), when the war was done,
     To mysteries strange and hateful rites returned:
     To you alone 'tis given the gods and stars
     To know or not to know; secluded groves
510  Your dwelling-place, and forests far remote.

- Lucan, Pharsalia I, 495-510 ( http://sunsite.berkeley.edu/OMACL/Pharsalia/book1.html)

(18) This Diana was worshipped by the Tauri, a people who dwelt in the Crimea; and, according to legend, was propitiated by human sacrifices. Orestes on his return from his expiatory wanderings brought her image to Greece, and the Greeks identified her with their Artemis. (Compare Book VI., 93.)
(19) The horror of the Druidical groves is again alluded to in Book III., lines 462-489. Dean Merivale remarks (chapter li.) on this passage, that in the despair of another life which pervaded Paganism at the time, the Roman was exasperated at the Druids' assertion of the transmigration of souls. But the passage seems also to betray a lingering suspicion that the doctrine may in some shape be true, however horrible were the rites and sacrifices. The reality of a future life was a part of Lucan's belief, as a state of reward for heroes. (See the passage at the beginning of Book IX.; and also Book VI., line 933). But all was vague and uncertain, and he appears to have viewed the Druidical transmigration rather with doubt and unbelief, as a possible form of future or recurring life, than with scorn as an absurdity.

This particular version also includes the caveat: "It should be noted that, as history, Lucan's work is far from being scrupulously accurate, frequently ignoring historical fact for the benefit of drama and rhetoric. For this reason, it should not be read as a reliable account of the Roman Civil War."

From Proinsias MacCana:

Tuetates, Esus, Taranis: 'Mars', 'Jupiter'

In the first century A.D., Lucan mentions three deities by their Gaulish names (De Bello Civili I, 444-6): 'Cruel Teutates propitiated by bloody sacrifices, and uncouth Esus of the barbarous altars, and Taranis whose altar is no more benign than that of Scythian Diana'. He is evidently bent on titillating his metropolitan public at the expense of the Gauls, and one must allow for considerable exaggeration and misplaced emphasis. However, his mention of the cruel sacrifices by which these gods were appeased is taken up and expanded by a commentator writing centuries later, and these additions have generated much scholarly discussion and many conflicting theories.

According to one of the sources cited by the later writer the victims of Teutates were asphyxiated by being plunged head foremost into a full vat, those of Esus were suspended from trees and ritually wounded, and those of Taranis were burned, numbers of them together in cages of wood. Obviously these details were not invented by the commentator, but one cannot be sure that he cites them in their true context. The sacrifice to Taranis echoes Posidonius (as followed by Caesar and others), who reported in the first century B.C. that the Gauls burned numbers of human victims in huge wicker-work images. The sacrifice to Esus is not clearly defined, but it may be the remnant of a myth similar to that of the Germanic Odin who hung on the World Tree for nine days and nine nights and whose victims were likewise left hanging on trees.

The account of the Teutates rite recalls a scene pictured on the famous Gundestrup cauldtron, but the connection once assumed has latterly been called in question. It has also been compared with the death by drowning in a vat of mead, beer or wine which is ascribed by legend to the two Irish kings Dairmaid mac Cerbhaill and Muirchertach mac Erca as well as to the Norse Fjolnir. In the Irish legends the king is wounded, the house in which he is trapped burned down about him, and he finally perishes in a vat of liquor while attempting to escape from the flames. The fact that this elaborately contrived death takes place at Samhain, the sacred festival marking the end of summer, suggests that we have to do here with a recurrent mythological theme and, more specifically, with a rite relating to the sacred kingship. At the same time, it is to be noted that these Irish narratives belong to the well-known motif of the Threefold Death in which a person fulfills an unlikely prophecy by suffering three different deaths, in these cases by wounding, burning and drowning. The exact relationship between the international motif and the rite or rites recorded by the commentator of Lucan therefore remains to be explained.

The commentartor's two main sources disagree about the Roman equivalent of Teutates, the one equating him with Mercury, the other with Mars. These late identifications are probably without significance, but it does happen to be true that the Gaulish Mars and Mercury tended to be assimilated and their functions overlap. Thus we find the epithets Iovantucarus and Vellaunus applied to both deities. And just as Mercury-Lugh is a god of warrior prowess as well as of arts and crafts, so, despite Caesar, the Mars of Gaulish inscriptions is more than a god of war: he is a god of healing, fertility and protection, the guardian of his people and of their material prosperity whether against disease or against hostile arms. It is not surprising, therefore, that on some inscriptions he is qualified as Teutates, that is to say, as the tutelary god of the tribe: as already remarked, teutates appears originally to have been a descriptive term rather than a proper name, though it may well have evolved towards the latter.

Esus figures in the guise of a wood-cutter on two reliefs of the first century A.D. (pages 32 and 35), but while theres are of great interest and must reflect some episode from myth, unfortunately they lend themselves to an inordinately wide range of interpretations. It is difficult to estimate how widespread was his cult; his name occurs for certain in only one inscription.

For Taranis the evidence is a little more substantial. His title designates him as the 'Thunderer', and in several dedications he is expressly identified with Jupiter. The particularly Celtic attributes of this Gallo-Roman Jupiter are his wheel, which may be either a lightning or a solar symbol, and, less frequently, the spiral which represents the lightning flash. Wherever we find this god -- and he is attested throughout the Romano-Celtic area -- it seems reasonable to equate him with the god known as Taranis.

It does not follow, however, that he was universally known by this particular name; in fact it is unattested as a proper name in Irish, while Welsh has only two instances which are of uncertain relevance. Neither can it be said that insular traditions retains any clear reflection of such an individualized god. Irish deities are commonly assigned marvelous weapons and these have sometimes been regarded as symbolising the divine thunderbolt, but even if this were justified, the fact remains that these Otherworld arms are not the attribute of any single god. On the other hand , the Irish evidently set great store by the power of the elements. Solemn oaths were sworn under the sanction of sun and moon, water and air, etc., and are followed by swift retribution if violated.

In the great saga of Tain Bo Cuailnge (The Cattle-Raid of Cuailnge), when the Ulstermen are rebuked by the severed head of Sualtaimh for their tardiness in coming to the support of the hero Cu Chulainn as he stands alone in defence of the province, Conchobhar their king makes this reply: 'A little too loud is that cry, for the sky is above us, the earth is beneath us and the sea all around us, but unless the sky with its showers of stars fall upon the surface of the earth or unless the ground burst open in an earthquake, or unless the fish-abounding, blue-bordered sea come over the surface of the earth, I shall bring back every cow to its byre and enclosure, every woman to her own abode and dwelling, after victory in battle and combat and contest'. The mentality here revealed is of great antiquity: it is, for example, that of the Adriatic Celts who, when they were asked by Alexander the Great what they feared most, are reported to have said -- with a disarming candour -- that they feared no one unless it were the sky that might fall upon them.

-MacCana, Proinsias. Celtic Mythology (p. 29-32)



There is also a figurine in the same book, which is basically the main representation of Taranis, with the following description:

Far right
Bronze figure of the Gallo-Roman Jupiter, from Chatelet (Haute-Marne). As well as the Greco-Roman thunderbolt he carreis the Celtic spiral-symbol and his left hand rests upon the wheel which is the emblem of the Celtic Taranis, 'The Thunderer'. Musee St. Germain-en-Laye.

(description p. 34, figure p. 35)