The municipality of Erto and Casso, situated in the Vajont Valley, is located in the province of Pordenone on the border with the province of Belluno. The existence of Erto is well documented by ancient excerpts from the Roman age and by a donation act from Sesto al Reghena which dates back to the 8th century, while the more recent origin of Casso is confirmed in the 11th century.
There are considerable linguistic differences between the two towns: Erto speaks a dialect that lies somewhere between Dolomite Ladino and Friulian, while in Casso there exists a Veneto Bellunese dialect, which is similar to the archaic Veneto dialect. Also, from an ecclesiastical point of view, the two villages are separate: Erto is part of the diocese of Pordenone, while Casso resides within the diocese of Belluno-Feltre.
Until the end of 1950s the community was profoundly linked to the traditional agricultural economy, integrated with small itinerant trade.
Between the 1950s and 1960s, Società Adriatica di Elettricità (SADE) developed a project to use the Vajont valley as a water reservoir. In 1960, at the start of the first reservoir test, two landslides occurred. As a result, the unstable slope of 200 hectares was in need of constant monitoring. The reservoir was tested again, with a second filling in 1962 and a third test the following year. Despite the imminent landslides, no adequate measures were taken to protect the inhabitants.
On the night of October 9, 1963, from the nearby Mount Toc, located opposite the hamlets of Erto and Casso, part of the mountain broke off and fell into the reservoir below bordered by the Vajont dam. The resulting waves completely destroyed nearby villages and part of the two municipalities.
This tragic episode, resulting in 347 victims in Erto and Casso, is known as the Vajont disaster.