In 1963, Italy completed the Vajont Dam, a double-curvature arch dam that stood 262 meters (859 feet) high, making it the tallest dam in the world at the time. Constructed between 1956 and 1960, the dam surpassed the height of the Hoover Dam in the United States by more than 100 feet. However, the structure's legacy was marred by a catastrophic event on October 9, 1963, when a massive portion of Mount Toc collapsed into the reservoir in the Italian Dolomites. The sudden collapse triggered a colossal wave that surged over the dam and devastated five villages downstream. The disaster claimed approximately 2,000 lives, with 260 million cubic meters of rock falling in just 45 seconds. In Longarone, one of the hardest-hit villages, nearly 94 percent of the population perished. Geological concerns had been raised as early as 1959, when geologist Edoardo Semenza identified signs of ancient landslides on Mount Toc, suggesting the possibility of a massive rockslide. Despite these warnings, the dam was completed and eventually became state-owned in 1962 following the nationalization of Italy’s electrical industry. As the reservoir filled, the mountain’s slope became increasingly unstable. By early October 1963, the southern slope of Mount Toc moved nearly a meter in a single day. Although a partial evacuation was ordered on October 8, it was limited to those living directly on the slope or below 730 meters in altitude. The landslide occurred on October 9, with the wave destroying five towns—Longarone, Pirago, Rivalta, Villanova, and Faè—and affecting nearby areas such as Erto and Casso. The death toll varied between 1,900 and 2,500, with over 1,400 victims in Longarone alone. Despite the massive destruction, the dam itself suffered minimal damage and still holds two-thirds of the water from the reservoir. The disaster occurred before the dam was even used for its intended purpose of generating electricity. Investigations later identified three main causes: a hidden slip plane in the rock, unfavorable geological conditions, and the reservoir’s water lubricating the clay layers of the slope. Carlo Semenza, the chief engineer of the project, who had died in 1961, was posthumously cleared of responsibility by a court in L'Aquila. A memorial in Longarone lists the names of 1,917 villagers who died in the disaster. The town was rebuilt and now thrives as a flourishing community. Today, the Vajont Dam stands as a somber reminder of the tragedy, serving as a site for memorial tourism rather than a source of electricity. The structure remains intact, though it never fulfilled its original purpose of powering the region. The disaster remains a cautionary tale about the intersection of engineering, geology, and the risks of large-scale infrastructure projects in geologically unstable areas.