An evocative monumental square, the current Piazza della Repubblica was formerly known as Piazza Esedra. The name derives from the large exedra of the Baths of Diocletian, whose perimeter is traced by the semicircular colonnade designed in the late 19th century by Turin architect Gaetano Koch, who also designed the majestic buildings that frame it. Overlooking the square is the Basilica of Santa Maria degli Angeli e dei Martiri, a masterpiece by Michelangelo created from a wing of the baths complex. Inside, the splendid floor features the Sundial (or Clementine Line), enriched with marble inlays depicting the signs of the zodiac and constellations.

The center of the square is dominated by the Fountain of the Naiads, a display of the Acqua Marcia, a water conduit built in 144 BC by Quintus Marcius Rex. The fountain's final installation was decided in 1885, as part of the new Master Plan, to serve as a dramatic backdrop to Via Nazionale. The decorative project, entrusted to Mario Rutelli in 1897, includes four bronze groups of nymphs reclining on aquatic animals, symbols of the different forms of water: a seahorse (Oceans), a serpent (Rivers), a swan (Lakes), and a lizard (Subterranean Rivers). At the time, the prominence of the female nudes sparked heated controversy, so much so that the work remained hidden behind a wooden fence for a long time. The central group also drew criticism: the original (composed of tritons, a dolphin, and an octopus, now visible in Piazza Vittorio Emanuele II) was eventually replaced with the current Triton embracing a dolphin.