The northern part is situated on the southern foothills of the Colli Albani range and was geologically formed about 150,000 years ago, after the collapse of the Volcano Laziale (caldera).

On the other hand, the southern boundary forms around Pontine Marshes, whose reclamation started at the time of Pope Pius VI and was accomplished during the regime of Benito Mussolini.

According to the classification given by the Geological Survey of Italy,[4] much of the territory consists of ground-type LPS, or paleosols, the rest is mainly composed of soils lp, lapilli, argillificate, Mafic, and leucite analcimizzata.

The area west of the walled city is a bit higher at San Lorenzo reaching 372 m (1,220 ft) above sea level.

The remainder of the territory to the south and west is basically flat except for small hills that do not exceed 300 m (984 ft) above sea level.

[6] The climate of Velletri is mild, due to the Tyrrhenian Sea not being far, and to the protection offered by the Alban Hills and Mount Artemisio in the north.

Humid currents from the southwest facing the Mont Artemisio condense all the rain on Velletri, leaving clouds restricted to the northern side of the Colli Albani.

[8] In the Middle Ages, at least six naming variants (Velletrum, Veletrum, Veletra, Velitrum, Bellitro, Villitria) are attested by various official acts until the 11th century.

[8] During his reign (642–617 BC), Ancus Marcius, the fourth king of Rome, came into conflict with the Volsci because the latter plundered Roman territory.

The colonists sent envoys to Rome "to clear themselves of the charge of joining in the Volscian war and to ask for the release of the captives, that they might punish them in accordance with their own laws".

The siege lasted until 367 BC when Marcus Furius Camillus, after defeating a force of Gauls which had encamped near Rome, captured the town, which surrendered without a struggle.

It was decreed that if a Veliternian senator crossed this river, "his redemption should be set at a thousand pounds of bronze, and that he who had captured him might not release his prisoner from bondage until the fine was paid".

[16] According to Cornell and Oakley, Velitrae and Lanuvium were incorporated into the Scaptia and Maecia respectively, thus obtaining Roman citizenship.

Augustus was born at the Ox Head, a small property on the Palatine Hill in Rome, but spent his childhood in Velitrae.

Suetonius wrote that "A small room like a pantry is shown to this day as the emperor's nursery in his grandfather's country-house near Velitrae, and the opinion prevails in the neighbourhood that he was actually born there.

The entire area of the Alban Hills and the Monti Prenestini was dominated by the Counts of Tusculum, including the fortress of Lariano next to Velletri.

In 1084, Robert Guiscard marched against Rome and passed through Velletri, meeting resistance from residents, who were rewarded by the Pope in 1101, with a Breve that gave very broad boundaries to the Veliterna community.

In 1434, during the struggle against the Colonna and Savelli families, Pope Eugene IV razed the castle of Lariano with the assistance of 800 Velletrani soldiers.

On April 21, 1482, during the Salt War between Pope Sixtus IV and Ferdinand of Aragon 500 Velletrani soldiers, 250 of whom were considered to be among the best Italian archers, fought with the papal army of Roberto Malatesta in the Battle of Campomorto, in a marshy area next to the territory Velletri, now in the town of Aprilia.

The 36th U.S. Infantry Division commanded by General Fred Walker spotted a flaw in the German defenses on Mount Artemisio between Velletri and Valmontone.

On 14 June 2001, Mario Pepe of the Chamber of Deputies[clarification needed] presented a bill on the establishment of the province of the Castelli Romani with Velletri as its capital .

In the proposal the following municipalities would be part of the new province: Albano Laziale, Anzio, Ardea, Ariccia, Artena, Carpineto Romano, Castel Gandolfo, Cave, Colleferro, Colonna, Gavignano, Genazzano, Genzano di Roma, Grottaferrata, Lanuvio, Lariano, Marino, Monte Compatri, Montelanico, Monte Porzio Catone, Nemi, Nettuno, Olevano Romano, Palestrina, Pomezia, Rocca di Papa, Rocca Priora, San Cesareo, San Vito Romano, Valmontone, Velletri, and Zagarolo.

On 23 September 2007, Pope Benedict XVI, who as Cardinal Bishop had the title of Velletri-Segni, visited Velletri celebrating a Mass in Piazza San Clemente.

The existence of a Roman amphitheatre in Velitrae is attested to by a curve in area adjacent to the Town Hall and an inscription found in the 1565.

There are other green areas: the recently restored Gardens of St. Mary, in the suburbs towards Nettuno, which has an ice skating rink, fountains and a bar, and the Muratori Park.

It has several book collections assembled by individuals from the 18th century and is an integral part of SBCR (Library System of the Castelli Romani).

A College of the Society of Jesus was established in Velletri by the papal bull of Pope Pius IX, Quod Divina Sapientia on April 7, 1851.

The Giancarlo Vallauri Istituto Tecnico Industriale Statale is a technical school which was founded in 1960 as a branch of the Enrico Fermi Institute of Rome.

with Ostia's severe loss of population, the university was moved to Velletri, where form 1817 it run humanities courses which led to degrees.

The sports hall host the cities basketball and volleyball teams, It opened in December 2008, and it is located in San Biagio.