At Piazza del Mercataccio (so named because the market was held there until 1819), one can admire this Roman retaining wall built to support and contain the massive amount of land on the eastern slope of the hill of Todi. The four grandiose vaults are 11 meters high and have an opening of 4.6 meters. They are topped by a beautiful sculpted entablature, which serves as a cornice with Doric-style decorations. Bas-reliefs adorn the metopes and triglyphs, architectural elements featuring human faces, animals, weapons, and bucrania (skulls of oxen).