It is situated on the site of the ancient Suessa Aurunca, on a small affluent of the Liri. The hill on which Sessa lies is a mass of volcanic tuff.
The town contains many ancient remains, notably the ruins of an ancient bridge in brickwork of twenty-one arches, of substructures in opus reticulatum under the church of S. Benedetto, of a building in opus quadratum, supposed to have been a public portico, under the monastery of S. Giovanni, and of an amphitheatre.
The Romanesque cathedral is a medieval basilica with a vaulted portico and a nave and two aisles begun in 1103, a mosaic pavement in the Cosmatesque style, a good ambo resting on columns and decorated with mosaics showing traces of Moorish influence, a Paschal candelabrum, and an organ gallery of similar style. The portal has curious sculptures with scenes from the life of Saint Peter and Saint Paul. In the principal streets are memorial stones with inscriptions in honour of Charles V, surmounted by an old crucifix with a mosaic cross. The hills of Sessa are celebrated for their wine.