In the course of Romanization, the Celtic polytheism of the local tribes was merged - syncretized - with the Roman religion. The Celtic deities came to be worshiped under the names of their Roman counterparts. Thus Lugus was replaced by Mercury, Belenus by Apollo, Taranis by Jupiter and so forth, in a practice called interpretatio romana by Caesar, who pioneered it. Roman gods also acquired the names of local gods as epithets; thus Mars was venerated as Mars Caturix, Mercury as Mercurius Cissonius and Jupiter as Jupiter Poeninus after the god of the Pennine Alps.