Mentana's name in ancient times was Nomentum, to which the Via Nomentana led from Rome. According to Livy, the town was part of the Latin League, which went to war with Rome during the reign of Rome's king Lucius Tarquinius Priscus. Nomentum was one of a number of towns captured by Tarquinius. It was a Latin town, but was considered by some to be Sabine, and, like Fidenae and Ficulea, was excluded from the first region by Augustus, who made the Anio river its northern boundary. The city was part of the League defeated by Rome in the Battle of Lake Regillus, and was captured definitively in 338 BC. Subsequently, Nomentum received the civitas sine suffragio; in its municipal constitution the chief magistrate even in imperial times bore the title of dictator. Pliny and Martial often praise the fertility of its neighbourhood. Seneca the Younger affirmed in multiple occasions having property and retreating to Nomentum . In 741 it was briefly occupied by the Lombards and the inhabitants moved to a new centre on the Via Nomentana which was more easily defendable. On 23 November 799, it was the site of the meeting of Pope Leo III and Charlemagne. The Castle of Nomentum was a possession of the Roman family of the Crescenzi in the 10th and 11th century. In 1058 it was destroyed by the Normans and the population was drastically reduced. The castle was acquired by the Capocci family and, later, the Holy See entrusted it to the Benedictine monks of San Paolo fuori le Mura. In the 15th century it was under control of the Orsini family. In 1484 it was damaged by an earthquake. In 1594 it became a fief of the Perett family, first under Michele Perett of Venafro, and then in 1655 it came under the control of Marcantonio Borghese and the House of Borghese. On 3 November 1867 the city was the site of the Battle of Mentana between French-Papal troops and the Italian volunteers led by Giuseppe Garibaldi, who were attempting to capture Rome in order to incorporate it into the newly unified Kingdom of Italy. The battle ended in a victory by the French-Papal troops. In Mentana, the monument Ara dei Caduti is built over the mass grave of the Italian patriots who died in the battle.
The diocese was nominally restored as a Latin Catholictitular bishopric in 1966. It has had the following incumbents, of the lowest and once archiepiscopal ranks :
