The Basilica of Vitruvius has been discovered in Fano, Italy. Vitruvius was the great Roman architect of the first century BCE.
The basis for the claim is Vitruvius himself, who described this specific building in De Architectura, the only structure he attributes to himself.
https://arkeonews.net/archaeologists-confirm-fano-discovery-as-vitruvius-legendary-basilica-a-turning-point-for-classical-architecture/
Archaeologists state that the uncovered ruins correspond to the proportions, layout, and architectural features Vitruvius described for the basilica. These features include a rectangular public building, along with consistent dimensions and structural elements.
Here is Vitruvius’ description of the structure:
https://share.google/JZKoQhGBTuwm3QfVw