Legends have piled up around the name of Arzignano, and scholars have gradually taken them apart: the one about a temple to the god Janus, Arx Jani, has no archaeological support at all, and the theory of a Roman noble called Argenius, owner of the estate, does not stand up to serious scrutiny either. The derivation from the Venetian arzere, embankment, seems sounder: a name that tells of centuries of struggle by valley-floor farmers against the floods of the Chiampo stream, as with the similarly named towns of Arzergrande and Cavarzere, all founded on the banks of turbulent rivers. Above the hamlet of Castello, the San Matteo plateau still holds the squared boulders of a Bronze Age hillfort, older than the Scaliger stronghold built on the remains of a Roman fortification.
In January 1413 that stronghold was besieged by Hungarian troops under Pippo Spano, in the pay of king Sigismund at war with Venice. The people of Arzignano, running out of food, had only one resort left: a vow to saint Agatha, and on the fifth of February, the day of her death, the siege was lifted, perhaps tricked by the stratagem of throwing grain and food from the walls to fake abundant supplies. Ever since, a procession in medieval costume renews that vow every year, offering wax and silver ducats to the parish of Saint Agatha, and it has given rise to a twin-town bond with Catania, the saint's birthplace. Today the valley lives above all on leather tanning, an industrial district that has transformed the landscape of the Chiampo valley.