The dam was conceived in the 1920s and eventually built between 1957 and 1960 by Società Adriatica di Elettricità, at the time the electricity supply and distribution monopoly in northeastern Italy.

This event occurred after ENEL and the Italian government concealed reports and dismissed evidence that Monte Toc, on the southern side of the lake, was geologically unstable.

[citation needed] The dam was built by Società Adriatica di Elettricità (SADE), the electricity supply and distribution monopoly in northeastern Italy.

The "tallest dam in the world", across the Vajont Gorge, was conceived in the 1920s to harness the Piave, Mae, and Boite Rivers, to meet the growing demand for power generation and industrialization.

[citation needed] SADE stated that the geology of the gorge had been studied, including analysis of previous landslides, and that the mountain was held to be sufficiently stable.

This led to further studies in which three experts separately told SADE that the entire side of Monte Toc was unstable and was likely to collapse into the basin if the filling were completed, due to the raised water level increasing the instability.

Instead of heeding these warning signs, the Italian government chose to sue the handful of journalists reporting the problems for "undermining the social order".

In April and May 1962, with the basin water level at 215 m (705 ft), the people of Erto and Casso reported five "grade five" Mercalli intensity scale earthquakes.

[citation needed] In July 1962, SADE's own engineers reported the results of model-based experiments on the effects of further landslides from Monte Toc into the lake.

After the discovery of the landslide on the northern slopes of Monte Toc, it was decided to deepen the studies on these effects: The study of point 1 was performed at the Experimental Institute for Models and Structures (ISMES) of Bergamo, while for the others, the SADE decided to build a physical-hydraulic model of the basin, in which to perform some experiments on the effects of a landslide fall in a reservoir.

The first series of five experiments began on 30 August 1961, with a sliding surface of the flat landslide inclined by 30°, consisting of a wooden plank covered with a sheet.

To simulate the compactness of the moving material (which in the model remained the gravel), rigid sectors were inserted that were towed by ropes pulled by a tractor.

In the second set of 17 experiments, conducted from 3 January 1962, to 24 April 1962, the "collapsing" material was still gravel, this time held in place by hemp nets and cords.

One went upwards, reached the houses of Casso, fell back onto the landslide, and travelled onwards to dig the basin of the pond of Massalezza.

[19] Firefighters who set out from Belluno, after reports of the raising of the level of the Piave, could not reach the location, since from a certain point onwards, the road coming from the valley had been completely swept away.

[20] The firefighters from 46 Provincial Commands also participated in the rescue, with 850 men, including divers, land and helicopter teams, and many vehicles and equipment.

[citation needed] Immediately after the disaster, the government (which owned the dam), politicians, and public authorities insisted on attributing the tragedy to an unexpected and unavoidable natural event.

Indro Montanelli, then the most influential Italian journalist and a vocal anticommunist, attacked l'Unità and denied any human responsibility; l'Unità and the PCI were dubbed "jackals, speculating on pain and on the dead" in many articles by La Domenica del Corriere and a national campaign poster paid for by the Christian Democracy, the party of Prime Minister Giovanni Leone.

[24] The campaign accused the PCI of sending agitprops into the refugee communities, as relief personnel; most of them were partisans from Emilia Romagna who fought on Mount Toc in the Second World War and often had friends in the stricken area.

A few months after he lost the premiership, he became the head of SADE's team of lawyers, who significantly reduced the amount of compensation for the survivors and ruled out payment for at least 600 victims.

[26][27] The DC's newspaper, La Discussione,[28] called the disaster "a mysterious act of God's love", in an article that drew sharp criticism from l'Unità.

Survivors were entitled to "business start-up" loans, public subsidies, and 10 years of tax exemption, all of which they could "sell on" to major companies from the Venice region.

The dam, now owned by ENEL, was partially opened to the public in 2002 with guided tours and access to the walkway along the top and other locations.

In September 2006, an annual noncompetitive track event, called "Paths of Remembrance", was inaugurated, which allows participants to access some locations inside the mountain.

On 12 February 2008, in launching the International Year of Planet Earth, UNESCO cited the Vajont Dam tragedy as one of five "cautionary tales" caused by "the failure of engineers and geologists".

A joint production of Italian and French companies, it was titled Vajont—La diga del disonore ("Vajont—The Dam of Dishonour") in Italy, and La Folie des hommes (The Madness of Men) in France.