"All the people of Gaul are very religious. The god they honour most is Mercury. His statues are the most numerous. They consider him to be the inventor of all the arts. He is for them the god who shows them the path to follow, who guides the traveller. It is he who is most capable of making them money and of protecting their business.
"Next to him they worship Apollo, and Mars, and Jupiter, and Minerva; respecting these deities, they have for the most part the same belief as other nations: that Apollo averts diseases, that Minerva imparts the invention of manufactures, that Jupiter possesses the sovereignty of the heavenly powers; that Mars presides over wars. To him, when they have determined to engage in battle, they commonly vow those things which they shall take in war. When they have conquered, they sacrifice whatever captured animals may have survived the conflict, and collect the other things into one place." --De Bello Gallico
Ah, but who are these gods, once divested of their Roman names? And are there more than six?
Well, scholars have conjectured that the following are the equivalent Gallic (ie continental Celtic) Gods:
ROMAN GALLIC WELSH IRISH
Mercury Lugos/Esus Lleu/Manawyddan1 Lugh/Cuchulain/Manannan mac Lir
Apollo Belenos Beli/Mabon ap Modron Bile
Mars Teutates Nudd? Nuada
Jupiter Taranos 2 the Dagda
Minerva Brigantia Sulis3 Brigit
Dis Pater Cernunnos? Arawn? Donn
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Not mentioned by Caesar, but mentioned by others, or monuments found:
ROMAN GALLIC WELSH IRISH
Hercules Ogmios Menw Ogma
Venus Epona Rhiannon/Branwen Macha
1. Manawyddan/Manannan mac Lir is sometimes considered a god of commerce, and a trickster god, particularly in Irish myth. Both Lugh and Cuchulain are fostered by Manannan, as Pryderi is by Manawyddan.
2. While there is no direct equivalent to Jupiter in Welsh myth, there is mention of a Glineu ap Taran, Taran meaning "Thunder." Elsewise, one may consider Bran.
3. A direct equivalent to Brigit doesn't exist in known Welsh myth, but it was likely a name similiar to Brigantia; her temple was at Bath.