The Battle of Mentana unfolded in the context of the Italian unification movement known as the Risorgimento, where various nationalist leaders sought to unite Italy under a single government. Giuseppe Garibaldi, an iconic figure of this movement, aimed to capture Rome and eliminate the Papal States, which were seen as obstacles to Italian unity. In 1867, Garibaldi's ambition led to a campaign to seize control of Rome, which was still under the rule of Pope Pius IX and supported by French military protection. As Garibaldi and his force of about 5,000 men approached Mentana, they encountered approximately 7,000 papal soldiers reinforced by French troops commanded by General de Failly.

The battle commenced on November 3, where Garibaldi's troops attempted to outmaneuver the papal forces. Despite their initial attempts to engage, the poorly organized Italian volunteers faced intense artillery fire and well-coordinated assaults from the papal army. The French intervention proved significant, bolstering Papal forces and resulting in Garibaldi's forces being decisively overwhelmed. After several hours of combat, Garibaldi's men were forced to retreat, suffering significant casualties and ultimately failing to secure Rome. Following this defeat, Garibaldi’s aspirations for an immediate Italian Republic were severely diminished, although the goal of unifying Italy would ultimately be achieved a few years later in 1870, when the Papal States were annexed.