Sicarii is a term applied, in the decades immediately preceding the destruction of Jerusalem in 70 AD, to the Jewish Zealots, who attempted to expel the Romans and their partisans from Judea, even resorting to murder to obtain their objective. Under their cloaks they concealed sicae, or small daggers, from which they received their name. At popular assemblies, particularly during the pilgrimage to the Temple Mount, they stabbed their enemies or, in other words, those who were friendly to the Romans, lamenting ostentatiously after the deed and thus escaping detection.

The victims of the Sicarii included Jonathan the High Priest, though it is possible that his murder was orchestrated by the Roman governor Felix. Some of their murders were met with severe retaliation by the Romans on the entire Jewish population of the country. In other instances, they could be bribed to spare their intended victims. Even convicted Sicarii were occasionally released on promising to spare their opponents. Once, after kidnapping the secretary of Eleazar, governor of the Temple precincts, they agreed to release him in exchange for ten of their captured comrades.

At the beginning of the Jewish Revolt (66 AD), the Sicarii, with the help of other Zealots, gained access to Jerusalem and committed a series of atrocities, in order to force the population to war. In one account, given in the Talmud, they destroyed the city's food supply, so that the people would be forced to fight against the Roman siege instead of negotiating peace. Their leaders, including Menahem ben Jair, Eleazar ben Jair, and Bar Giora, were important figures in the war, and Eleazar ben Jair eventually succeeded in escaping the Roman onslaught. Together with a small group of followers, he made his way to the abandoned fortress of Masada, where he continued his resistance to the Romans until 73 AD, when the Romans took the fortress and found that all of its defenders had committed suicide rather than surrender.

Based on a 1903 Jewish Encyclopedia, with some additions and editing.