Cittanova was founded at the beginning of the 9th century as
Civitas Nova Heracliana (New City of Eraclea) on the ruins of ancient Heraclia, destroyed during the clashes between the rival factions of the pro-Franks and the pro-Byzantines (804) and then by
Pepin (810). The initiative came from the Doge
Agnello Participazio, of a Heracleense family, who had a holiday palace built there. cutting off the head of the Sassanid
shah Khosrow II; Melidissa was renamed "Eraclea" in his honor. The end of the settlement came with the great flood of 1110, when the Piave changed its course, ending up flowing into the Cavallino and transforming the lands of Cittanova into a malarial swamp. In a short time, nothing remained of the ancient city, except the cathedral of San Pietro, periodically visited on the occasion of religious solemnities by the bishop, otherwise residing in Venice or in one of the nearby monasteries. The diocese was finally suppressed in 1440 and aggregated to the patriarchate of
Grado. San Donà passed from the diocese of Cittanova to that of Treviso in 1334. Between 1543 and 1664 the area was affected by the impressive hydraulic works ordered by the
Republic of Venice to avoid the swamping of its lagoon. The Piave was diverted and led to flow into a vast artificial freshwater lake near Cittanova called
Lago della Piave, where today there are the hamlets of
Passarella and
Palazzetto. The situation seemed ideal to favor the flourishing of the area, but not even twenty years later another flood pushed the river to assume its current course and it was necessary to wait till the end of the
First World War for the
bonifica of
Eraclea (the
Bonifica di Eraclea) to take place. ==Today==