1/2 Grosso - Pietro di Montebruno Sede Vacante, Uncertain mint

The sede vacante of 1268–1271 remains the longest papal interregnum in Church history — nearly three years during which the College of Cardinals, deadlocked in Viterbo, could not elect a successor to Clement IV. Pietro di Montebruno served as Rector of the Papal States during this vacuum, and coinage issued under his authority represents one of the few institutional functions that continued uninterrupted while cardinals literally died waiting for consensus. The conclave only broke when local authorities locked the electors in and reduced their food supply.