Aius Locutius (Latin: āius locūtius, spoken affirmation) or Aius Loquens (Latin: āius loquens, speaking affirmation), was a Roman deity or numen associated with the Gallic invasions of Rome during the early 4th century BC.
According to legend, a Roman plebeian named M. Caedicius heard a supernatural, nocturnal voice that issued from Vesta's sacred grove, at the base of the Palatine hill. It warned him of an imminent Gaulish attack, recommended that the walls of Rome be fortified and instructed him to pass these messages on to the tribune of the plebs; but because of the messenger's humble station, the message was ignored. In consequence, the Gauls entered and burned the city (c.391 BC). Once the Gauls were repelled, the senate built a temple and altar (known as Ara Aius Locutius, or Ara Saepta) to propitiate the unknown deity who had offered the warning. This was said to have been set up where Caedicius had heard the divine voice. Later Roman historians disputed its exact location and no trace remains of the temple or altar; the latter has been historically misidentified with the Palatine altar inscribed si deus si dea ("whether God or Goddess"), in cautious dedication to some unknown deity.
In the broad context of official Roman religion, Aius Locutius is exceptional. Officially, the gods might speak through the cryptic writings and utterances of specialised oracles, or through a complex system of signs in answer to the specific questions of State augurs. They might also grant signs of fortune to their most favoured protégés, or speak privately to them in dreams. Aius Locutius gave clear, urgent instructions of great importance to the State, in everyday Latin, to an ordinary plebeian passer-by – and thereafter, according to Cicero, "having acquired a temple, an altar, and a name, 'Speaker' never spoke again".
The epithet Locutius was also used to invoke one of the deities concerned with child development.