Hoover Dam's Secret

When the Hoover Dam was being drafted, engineers calculated that it would take 125 years for the concrete to cool if done in a single pour. Instead, they poured it in sectioned blocks, some as big as 50 square feet and 5 feet high. This way, the physical dam itself will survive up to 10,000 years and be one of the last remaining visible and recognizable monuments of humans on the planet. Also, the first death occurred on December 20, 1922, during its construction. Exactly 13 years later, on December 20th, 1935, the last death occurred, and the two men were father and son, respectively.