Why does Caesar’s use of Roman god names make Celtic gods difficult to identify?

In his Commentarii de bello Gallico, Julius Caesar identifies Gaulish deities by the names of Roman gods rather than their native names, a practice known as interpretatio Romana. This approach complicates the identification of Celtic gods for several reasons:12

• Functional Misalignment: Caesar imposes a neat, schematic equation of god and function that is often foreign to the nature of Celtic deities, who were not always rigidly compartmentalized. For example, a single Celtic god might possess multiple roles—such as sovereignty and warfare—leading to conflicting Roman interpretations where one commentator might equate a deity with Mercury and another with Mars.1
• Loss of Native Context: By substituting Roman names, Caesar obscures the specific cultural and mythological identities of the Gaulish figures, making it difficult to link them to counterparts found in later insular literatures (such as Irish or Welsh traditions).1
• Oversimplification: Caesar’s catalog provides a limited view that ignores the complexity of local and tribal cults. Because many Celtic deities were associated with specific regions or tribes, the use of broad Roman labels masks the diversity and nuance of the original religious landscape.1