In 338 BC, it was seized by the Roman soldiers and overcome by Furius Camillus, who destroyed the walls, which were rebuilt only in the 8th century as a defence against the Saracen marauders. Later, Velletri became a Roman municipium, and fought against Pyrrhus and Hannibal.

It then lived a splendid and peaceful period until the pax romana was interrupted in 410 by the invasion of Alaric’s Goths.

During the centuries, the town became a country residence for emperors and famous patricians. It was here that the Gens Octavia, the dynasty of Emperor Octavianus Augustus, originated. According to tradition, Velletri was converted to Christianity by a monk named Clement, who later in the year 88 became Pope of the Roman Catholic Church with the name of Clement I and today is the patron saint of the town.

Throughout the years, the town acquired more importance and was in excellent relationships with the Pontifical State. In 1088, the Conclave of Terracina elected pope Otho de Lagery, the Bishop of Velletri, who took the name of Urban II and promoted the First Crusade.

During the 8th century, Velletri was administered as a Republic. In 1298 Pope Boniface VIII, who before becoming pope was the Podestà of Velletri (Chief Magistrate of Velletri), freed the town from likely influence by the Pontifical Campagne and Maritime Province, making the town practically independent.

In 1408, Velletri was conquered by Ladislao The Magnanimous, King of Naples, who did however maintain the town’s independence. In the 16th century, it became part of the patrimonial possessions of the Church. During those years (1514), on a visit to Velletri, Raffaello painted la Madonna della Seggiola (Madonna of the Chair), inspired by a local countrywoman. In 1527, the Lansquenets on their way back from the famous Sack of Rome ransacked the town.

After this episode, Velletri had basically lost its political independence: in fact, in 1559, the Pope imposed the civilian government of Cardinal Bishop, the first of which was Giovanni Pietro Carafa, later appointed Pope Paul IV.

In 1744, the town witnessed the famous Battle of Velletri between the Austrian troops of Maria Theresa Habsburg and the Bourbons of Carlo di Borbone, whose armies fought on the land of the Castelli Romani, won by the Neapolitan soldiers. Signs of the battle remained for a long time on the territory and the bombed buildings and countless victims left a harsh sign in the town’s history.

In 1798, General Michele Pezza, so-called Fra Diavolo, with his band of rebels allied with the inhabitants of Velletri against the French. Velletri proclaimed the Republic.

In 1849, a difficult historic battle took place on the land of Velletri: the troops of the Roman Republic, commanded by Giuseppe Garibaldi won against Ferdinando II di Borbone, who was trying to approach Rome. A year or so later, Garibaldi asked to become a citizen of Velletri and his son Menotti Garibaldi settled in the town and held an administrative office.

In 1866, Pius IX inaugurated the railway line Rome-Velletri, the third railway line of the Pontifical State and one of the first in Italy. This was a great advantage for the growth of the town also after becoming part of the Kingdom of Italy in September 1870, and the unification with the Province of Rome. In 1885 the first modern bank was established, la Cassa di Risparmio di Velletri; in 1882 the first wine exhibition was held and at the time the Cantina Sperimentale (wine experimental centre) was established. In 1913, the first tramline of the Castelli Romani began at Velletri connecting the town directly with Rome and the other towns of the Castelli Romani. This route was in service until 1953.

During the Second World War, the town, positioned along the route of the Allied troops that were advancing from Anzio to Rome, was heavily bombed.

In 2005, Velletri saw for the 14th time its bishop rise to the status of Pope. The bishop in question was Cardinal Joseph Ratzinger who became Pope Benedict XVI.