The Altar of Domitius Ahenobarbus is a series of four sculpted marble plaques that probably decorated a base supporting cult statues in the cella of a Temple of Neptune located in Rome on the Field of Mars.

Gnaeus Domitius Ahenobarbus was a Roman general and senator who served as consul in 122 BC. He led a campaign to conquer southern Gaul against the Allobroges together with his successor Quintus Fabius Maximus Allobrogicus. Domitius was active in the early development of southern Roman Gaul, establishing the first Roman colony at Colonia Narbon Martius, and sponsored projects such as the Via Domitia connecting Italy to Spain through southern Gaul. He was probably also the sponsor of the Altar of Domitius Ahenobarbus in the Temple of Neptune in Rome. Ahenobarbus was censor in 115 BC and became pontifex at an unknown date before dying c. 104 BC.