Eraclea was first officially mentioned around 640, when it was appointed a new diocese, together with the island of Torcello, in a papal bull by Pope Severinus.

However, the history of this town began much earlier. Like nearby Jesolo, it was founded by the population of ancient Oderzo, fleeing the descent of the Gauls, who took refuge in the nearby lagoon area, creating the first settlement on the Island of Melidissa, which later became the town of Eraclea.

It was here that the powerful Oderzo (Opitergium) moved the Byzantine government during the Barbaric Invasions and the Bishop Saint Magnus found refuge here in 638 together with the most powerful families in the city.

The new town that was created was given the name Heraclia in honour of the Emperor of the East ERACLIO, who had stopped the expansion of the Longobard Barbarians in the Veneto Lagoon.  

Eraclea later became an important strategic point for commercial trade with both the Byzantine court and the Longobard court of Pavia.

The town of Eraclea is also remembered as the home of the first  Doge in the history of the Veneto. Important archaeological relics that testify to the great history of this little town are today preserved in various museums around the province.