At the beginning of the 20th century, people inspired by the big progress made by mankind through industrialization and science weren’t shy to think big. Like, really big.
German architect Herman Sörgel came up with the idea to build a hydroelectric dam across the Strait of Gibraltar and some additional dams, thereby lowering the surface of the whole Mediterranean Sea by 200 meters. The dam would provide electric power, and the lowering of the surface would open up formerly submerged lands for settlement and agriculture.
The perils of this venture though were barely assessable. The dam would be prone to tsunamis. It would have had a vast impact on the environment. The change in pressure on the plates may have caused shifts, volcanic eruptions and earthquakes. The surface of the other oceans might have raised for one meter. The impact on the economy of the surrounding countries due to change of borders and new trade routes was likely to be severe.