A Gaulish deity, widely worshipped by the continental Celts whose name is known from an inscription found at Beaucroissant, Isère, France where he is invoked as Mercury Artaius. The assimilation of Artaius into the Cult of Mercury by Interpretatio Romana has led many to suggest that Artaius was originally a pastoral deity, possibly associated with ovine protection.

The similarities in name between Artaius and the insular 'Arthur' have led to postulations that they originated as one and the same deity; indeed Arthur probably originated as a god who became fused with a historical personage in later tellings. Others have associated Artaius with the mage-deity Gwydion postulating that Artaius may originally been a god of the Great Wizard type.

Artos, the alternative name of this deity is preserved in the place names Arto-briga, near modern-day Weltenburg in Germany and Arto-dunum (fortress of the Bear, modern Arthun) in the Loire.

Artaius' name can be derived from the reconstructed proto-Celtic elements *arto- (bear) along with the deicitic particle *ī and the Latinized masculine ending -us. Thus Artaius' name can be interpreted as 'The Bear God'. Artaius has a female counterpart, Artio. Artaius' name is also cognate with that of Arthur. Though whether Artaius was the mythological equivalent of the insular Arthur may never be known.