Gaeta is a city and comune in the province of Latina, in Lazio, central Italy. Set on a promontory stretching towards the Gulf of Gaeta, it is 120 kilometres (75 miles) from Rome and 80 km (50 mi) from Naples.

The town has played a conspicuous part in military history; its fortifications date back to Roman times, and it has several traces of the period, including the 1st-century mausoleum of the Roman general Lucius Munatius Plancus at the top of the Monte Orlando.

Gaeta's fortifications were extended and strengthened in the 15th century, especially throughout the history of the Kingdom of Naples (later the Two Sicilies). Present day Gaeta is a fishing and oil seaport, and a renowned tourist resort. NATO maintains a naval base of operations at Gaeta.

Main sights include:

• The massive Aragonese-Angevine Castle. Its origins are uncertain: most likely it was built in the 6th century, in the course of the Gothic War, or during the 7th century to defend the town from the Lombards' advance. First documents mentioning it date to the age of Frederick II of Hohenstaufen, who strengthened it in 1233. The current structure is made of two different edifice: the "Angevine" one, in the lower sector, dating to the House of Anjou's rule in the Kingdom of Naples; and the "Aragonese", at the top, built by emperor Charles V, together with the other fortifications that made Gaeta one of the strongest fortresses in southern Italy. The Angevine wing housed a military jail until the 1980s (German war criminal officers Walter Reder and Herbert Kappler were imprisoned here). Now it is a property of the Gaeta municipality, which uses it for conferences and exhibitions. In the dome of the tallest tower is the Royal Chapel, built by King Ferdinand II of the Two Sicilies in 1849.
• The Mausoleum of Lucius Munatius Plancus (22 BCE) is a cylindrical travertine monument at the top of Monte Orlando (168 m). It stands at 13.20 m and has a diameter of 29.50 m. Another important Roman public man, Lucius Sempronius Atratinus, Mark Antony's fleet commander, has a mausoleum, sited in the more recent district of Gaeta: of similar diameter, it is however not as well preserved.
• The Sanctuary of SS. Trinità, mentioned as early as the 11th century and visited, among the others, by St. Francis and Saint Philip Neri. The Crucifix Chapel was built in 1434 over a rock which had fallen from the nearby cliffs. From the sanctuary the Grotta del Turco can be visited: it is a grotto which ends directly in the sea and where the waves create atmospheric effects of light.
• Sanctuary of Santissima Annunziata - A church and adjacent hospital were built at the site in the 14th century, but rebuilt at the beginning of the 17th century in Baroque style by Andrea Lazzari. It houses works by Renaissance painters including A Sabatini and GF Criscuolo; as well as late-Baroque artists such as Giordano, Conca and Brandi. The church has a Gothic-style sarcophagus of Enrico Caracciolo. Also notable is the Golden Chapel or Grotto, a Renaissance-style chapel where Pope Pius IX meditated before issuing the dogma of the Immaculate Conception. The ceiling is gilded, and the walls contain 19 canvases (1531) by Criscuolo. The main altarpiece is an Immacolata by Pulzone.
• San Giovanni a Mare - The church was initially built outside the old sea walls, by the hypate Giovanni IV in the 10th century. It combines the basilica form with the Byzantine one. The simple façade has a Gothic portal and a dome, while the interior has a nave with two aisles. The inner pavement is slightly inclined to allow waters to flow away in the case of maritime floods.
• The Cathedral of Assunta e Sant'Erasmo was erected over a more ancient church, Santa Maria del Parco, and consecrated by Pope Paschal II in 1106: it had a nave with six aisles separated by columns with Gothic capitals. In 1778, however, two of the aisles were suppressed and the Gothic lines hidden. In the 13th century Moorish arches were added over the capitals. In 1663 the crypt was decorated in Baroque style. The interior houses a banner from the Battle of Lepanto, donated by Pope Pius V to Don John of Austria, who used it as his admiral's flag. The main sight of the church is however the marble Paschal candelabrum, standing 3.50 m tall, from the late 13th century: it is in Romanesque style, decorated with 48 reliefs in 4 vertical rows, telling the Stories of the Life of Jesus. There are also paintings by Giacinto Brandi and Giovanni Filippo Criscuolo. The cathedral contains the relics of St. Erasmus, transferred from Formia; the remarkable campanile, in Arab-Norman style, dates from the 12th century. At the base are slabs and parts of columns from ancient Roman edifices.
• The Cathedral has a great bell tower, standing at 57 m, which is considered the city's finest piece of art. The base has two marble lions, and the whole construction made large reuse of ancient Roman architectural elements. The upper part, octagonal in plan, with small Romanesque arches with majolica decoration, was completed in 1279.
• The Chapel of the Crucifix is a curiosity: built on a huge mass of rock that hangs like a wedge between two adjoining walls of rock. Legend tells how the rock was thus split at the moment of Christ's death.
• San Francesco - According to the legend, the church was constructed by the Saint himself in 1222, was in fact built by Frederick II, in very fine Gothic-Italian style, and contains paintings and sculpture by many of the most famous Neapolitan artists.
• The parish church of Santa Lucia, the former St. Maria in Pensulis, was once a Royal chapel and here prayed Margherita of Durazzo and king Ladislaus. It had originally Romanesque and Sicilian-Arab lines, but in the 1456 it was rebuilt in Renaissance style, and in 1648 adapted to a Baroque one. The side has a Mediaeval pronaos with ancient fragments and figures of animals.
• The Medieval Quarter of Gaeta is itself of interest. It lies on the steep sides of Mount Orlando and has characteristic houses from the 11th-13th centuries.