One June day in 1331, Cassiano, collector of the dazio (customs duty) at the small port of Riva on Lake Garda, became suspicious of two newly-arrived strangers. They claimed to be dealers in wax candles from nearby Verona, but he thought they spoke in the wrong dialect. Instead of visiting a merchant, they asked directions to the home of Monda, widow of a local apothecary. Because of their style of hair and dress, and because Monda had a reputation for free-thinking, Cassiano convinced himself they must be heretics (pathari). Cassiano's colleague in the port offices encouraged his speculations, which only strengthened when the two strangers vanished from sight for two weeks. When they reappeared, Cassiano hurried off to report his suspicions to ser Bressanino di Niccolò di Val di Ledro, who was the local official of the inquisition in Riva. The town was too small for a permanent inquisitor, so Bressanino took the denunciation to the inquisitor's vicar, Federico da Mantova, guardian of the local Franciscan convent. Federico agreed to accompany Bressanino to the port, but refused to take action against the strangers, saying he had no idea who they were and he did not want to overstep his office. All Cassiano and Bressanino could do was wait until the next year, when Alberto da Bassano, inquisitor for the Trento diocese in which Riva fell, visited the town to hold a travelling inquisitio. By convention, this began with an invitation to citizens to report any knowledge of heresy, and a large number queued up to denounce their neighbours or enemies, who were then interrogated by the inquisitor or his vicar. In this case, many depositions survive – including that of Monda, who was eventually cleared of suspicion.

This incident throws valuable light on the practical organisation of inquisition against heresy in medieval Italy, a subject largely ignored by scholars. Although the inquisition as a weapon against heretics began to take shape from the late 1230s, there was only ever a handful of actual inquisitors in office. To maintain any kind of effective geographical oversight, they had to build, and depend on, a network of local agents, both secular and clerical. The Riva episode shows how this system worked.