In Gallo-Roman religion

Gallo-Roman religion

Gallo-Roman religion was a fusion of the traditional religious practices of the Gauls, who were originally Celtic speakers, and the Roman and Hellenistic religions introduced to the region under Roman Imperial rule. It was the result of selective acculturation....

, Ambisagrus was a Gaulish god worshipped at Aquileia

Aquileia

Aquileia is an ancient Roman city in what is now Italy, at the head of the Adriatic at the edge of the lagoons, about 10 km from the sea, on the river Natiso , the course of which has changed somewhat since Roman times...

 in Cisalpine Gaul

Cisalpine Gaul

Cisalpine Gaul, in Latin: Gallia Cisalpina or Citerior, also called Gallia Togata, was a Roman province until 41 BC when it was merged into Roman Italy.It bore the name Gallia, because the great body of its inhabitants, after the expulsion of the Etruscans, consisted of Gauls or Celts...

, where he was identified with Jupiter Optimus Maximus

Jupiter (mythology)

In ancient Roman religion and myth, Jupiter or Jove is the king of the gods, and the god of the sky and thunder. He is the equivalent of Zeus in the Greek pantheon....

.

The name may be composed of the Proto-Celtic prefix *ambi- ('around') and root *sagro-.

Dr. John Koch at the University of Wales Centre for Advanced Welsh & Celtic Studies has suggested that this Jovian epithet may originally have applied to Taranis

Taranis

In Celtic mythology Taranis was the god of thunder worshipped essentially in Gaul, the British Isles, but also in the Rhineland and Danube regions amongst others, and mentioned, along with Esus and Toutatis as part of a sacred triad, by the Roman poet Lucan in his epic poem Pharsalia as a Celtic...

, with allusion to the tendency of thunder near an observer to seem all-surrounding.