Elusa is the Aquitani-Roman city of the Elusates in Caesar's southwestern Gaul, the present-day town of Eauze in the Gers département.

The Elusates are mentioned by Julius Caesar in his Commentaries on the Gallic War, as one of the Aquitanian peoples defeated by his lieutenant Publius Crassus in 56 BC.

Their territory, augmented by that of the Sotiates, was chosen for the establishment of a city endowed with colonial-style Roman urban planning.

Elusa was founded at the beginning of the 1st century AD, 3 km south of the Elusates oppidum, on the first terrace overlooking the Gelise river.

Benefiting from the Pax Romana during the High Empire, the city prospered and reached a surface area of some 50 hectares.