Situated between the southern foothills of the Colli Albani and Agro Latium, near Rome, Velletri was an ancient city of Volsci, already influential at the time of Anco Marzio. The city's name has certain Latin roots "Velia" (swamp). The discovery of prehistoric tombs (like the tomb of tholos, found in the district of the Vigna d'Andrea) confirms that the area was inhabited since ancient times. The first permanent settlements date back to Etruscan times; stronghold of the Volsci (an ancient Italic population, that lived in the area south of Rome), was only conquered by the Romans in 338 B.C., who over the following years had to repeatedly stop and punish rebellions caused by the inhabitants of Velletri . During the X century, It became a possession of the Counts of Tusculum, until it was assigned to the Papal States and enjoyed a certain autonomy until 1559, when the Pope changed the law of the unification of the civil government to a temporary one. In 1744, Velletri was scenario of the battle of the War of the Austrian Succession between the troops of King Charles of Bourbon and those of Cristiano of Lobkowitz. In 1848 Giuseppe Garibaldi won, here, an important victory over the troops of Ferdinand II of Bourbon. During the Second World War the area was at the center of the clashes between the allied troops, that landed at Anzio, and the German ones lined up along the "Caesar line", suffering heavy losses.

Sites of Interest:
- the remains of the Volscian and Roman civilizations, now on display at the Diocesan Museum and at the Archaeological Museum;
- the remains of the Villa degli Ottavi, which belonged to the family the emperor Augustus;
- the Roman cisterns;
- the Basilica Cathedral of San Clemente, which according to ancient tradition, was already present in the V century. Profoundly altered and expanded over the centuries, today features three aisles divided by pillars of masonry stone, with a coffered ceiling and a raised presbytery, in which is placed an altar covered with a canopy supported by four granite columns with capitals in gilt bronze. The crypt houses the relics of Saints Pontian and Eleuterio;
- the Church of Santa Maria del Trivium, entitled to the Assunta, which owes its name to the circumstance of being located at the intersection of three main roads. Originally built in Gothic style, it was later demolished and rebuilt from designs of Carlo Maderno in 1622. The façade is in neo-Classical style and is flanked by the Tower of the Trivium, in Gothic style;
- the Church of San Martino, mentioned for the first time by Pope Alexander II in 1065;
- the Palazzo of the Town Hall, faithfully rebuilt after the bombings of World War II, according to the original XVI century drafts;
- Palazzo Vecchio, also faithfully reconstructed after the bombings of World War II;
- Porta Napoletana, built in 1511, consists of a main building and two side towers; it is the only remaining Renaissance gate entrance between the fortified city walls, which allowed access to the city.