The modern town occupies the site of the old one. The present Town Hall Square corresponds to the ancient Roman forum, and the Roman pavement of slabs of travertine with the inscription A. AEMILIUS A. F. in letters once filled in with bronze, is well preserved. The paving is supported by massive arched substructures, which extend under the surrounding houses.
Terracina Cathedral (Cattedrale dei SS. Pietro e Cesareo) is ensconced within an ancient Roman temple which was dedicated to the god Apollo; part of the side wall of which, with engaged columns, is still visible. The cathedral was consecrated in 1074, and restored in 12th and 18th centuries. Its relevance for Christianity is very high: here, in 1088, has been elected the Pope Urban II, who banned the First Holy Land Crusade in 1095.
The Cosmatesque-inlaid vestibule is preceded by an eighteen-step staircase, and supported by ten ancient columns resting upon recumbent lions, with a mosaic frieze upon them, made by 12th century Sicilian-Norman artists. The brick campanile, in Gothic-Romanesque-style, has small columns with little pointed arches and Islamic majolica in the walls. The interior has a Cosmatesque pulpit supported by ancient columns resting on lions, a Paschal candlestick of 1245, and a pavement of the same period with beasts and dragons.
The Gothic Palazzo Venditti, which is adjacent to the cathedral, was built from the first half of the 14th century. Nearby is also the Torre Frumentaria (“Wheat Tower”, 13th century), which now houses the Pio Capponi Local Museum.
The Town Walls consist of Byzantine and medieval towers, erected along the Volscian and Roman curtain wall, in “polygonal” style similar to those of Constantinople. Beyond a three-way crossing, next to Porta Nuova, is the Frangipane Castle or Rocca Traversa, which in 1202 became the symbol of the communal freedom of Terracina. It has been damaged by Allied bombing on September 4, 1943.
Other churches are those of the Annunziata (13th century, with a decorated architrave over the portal by a Master Andrew of Priverno), San Domenico (erected in the first decades of the 13th century, and enlarged in 1298) and San Francesco (1222), which follows the Gothic Cistercian style of the Fossanova Abbey (about 25 kms – 15.53 miles – far from Terracina).
Many Roman ruins were brought to light only after the World War II bombings. These include a quadrifrons (four-faced) arch, which served as entrance to the forum. Two sides can be still seen in good condition, 6.4 by 6.34 metres (21.0 by 20.8 ft) wide. Under it is a well-preserved stretch of the ancient Via Appia.
Above the town are several massive terrace platforms for supporting buildings; these may well belong to the Roman period, and the latter even to the Empire. The summit of the promontory called Mount Sant’Angelo (elevation 227 metres – 745 ft) is reached by the old line of the Via Appia, which is flanked by tombs and remains of an ancient defensive wall with circular towers, the so-called Cinta Sillana (once attributed to the Ostrogoth King Theodoric, but actually is dating from the first decades of the 1st century BC). The summit is occupied by a massive terrace, supported by arcades of fine opus incertum (traditionally, but wrongly, called “Theodoric’s Palace”) on all sides except the east, and commanding a magnificent view seaward over the coast and over the Pontine Marshes.
On the terrace stood the Corinthian Temple traditionally attributed to the god Jupiter Anxur (1st century BCE), about 35 by 20 metres (115 by 66 ft). The cella was decorated internally with engaged half-columns, and contained the pedestal for the statue of the Jupiter, who would have been venerated here as a child-god: this attribution is confirmed by the discovery of numerous leaden votive figures, like those made for dolls’ houses today, in the favissae on the east side of the temple. The interior cell measures 13 by 14 metres (43 by 46 ft) with 6 half-columns per side. However, recently the attribution of the temple to Jupiter has been put under discussion, due to the discovery of inscriptions dedicated to the goddess Venus.
Outside the temple is the Oracle, a kind of quadrilateral base with a hole from which, standing in a cave, the priests communicated the answers to the questions of the faithful. To the left of this great construction is the Small Temple, probably a civil building that, after Christianity has been declared as the official religion in the Roman Empire, was transformed in a monastery dedicated to St. Michael the Archangel.
Massive remains of another temple, the Capitolium, 16.5 by 16 metres (54 by 52 ft), with cells 9.5 by 4.5 metres (31 by 15 ft) wide, located on the street which starting from Palazzo Venditti. Built in the middle of the 1st century BC, it was dedicated to the Capitoline Triad of Jupiter, Juno and Minerva.
Of the lower town by the harbour, which had buildings of some importance of the imperial period (amphitheatre, baths, etc.), little is now visible, and its site is mainly occupied by a new borough built by Pope Pius VI in the late 18th century. About the ancient harbour constructed and enlarged by the Emperors Ulpius Trajan and Antoninus Pius, there are some largely silted up ruins. Close to it is the small modern port. Near the amphitheatre was found in 1838 the famous marble bust of Sophocles, now in the Lateran Museum, Rome.
Terracina includes also a considerable extent of territory towards the northwest with much undergrowth (macchia) valuable for charcoal burning, and a considerable extent of pasture and arable land. The ancient aquaeduct, bringing water for 55 kilometres (34 miles) from the slopes of the Volscian Hills, has been repaired and is in use. About 5 kilometres (3 miles) northwest, near Mount Leano, was the shrine of the nymph Feronia, where the canal following the Via Appia through the marshes ended. Along these three km of the Via Appia are numerous ancient tombs, and the fertile valley to the northeast was thickly populated in Roman days, before the intrusion of malaria.