Largo di Torre Argentina was named after Argentoratum—a Roman military outpost located in modern-day Strasbourg—and holds the remains of four temples from the Republican age (4th-2nd century BCE), yet because the identifications of such temples are not entirely certain, they are named with the first four letters of the alphabet—Temple A, B, C, and D.
Fun fact: behind temples B and C is a large tuff base with the remains of Curia of Pomey, which was a site where the Senate of Rome was held and where Julius Caesar was stabbed during the Ides of March.