60-STOREY DAM A CATHEDRAL THAT’S TAKEN OVER 140 YEARS TO BUILD

WONDER: Hoover Dam LOCATION: Arizona-nevada border WONDER: La Sagrada Familia LOCATION: Barcelona, Spain

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Even without knowing the history behind the Hoover Dam’s origins, the size of this giant water levee is enough to inspire awe. Even today, building a dam the height of a 60-storey building across one of North America’s biggest rivers would be technically challenging. And when the Hoover Dam was being constructed between 1930 and 1936, it was the largest dam ever built.

The Colorado River, which stretches 1,400 miles from Colorado’s Rocky Mountains to the Gulf of California, was once faster flowing, more direct and very unpredictable. It caused sudden flooding and regularly left the surrounding lands in drought. To convert the river into a reliable water source for the drier southwest region of the US, the Hoover Dam was built. Construction commenced during the

Great Depression, resulting in thousands of people travelling many miles to the Hoover Dam looking for employment. Workers scaled the rocky canyon, inserting dynamite into the rock by hand to break away the foundations. Despite the treacherous working conditions, which caused around 100 men to fall to their deaths, the Colorado River was eventually tamed by the dam. Today this dam is one of the world’s largest hydroelectric power plants.

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On 19 March 1882, Spanish architect Francisco de Paula del Villar launched the building of La Sagrada Familia basilica. His part in the project would be over when he resigned from the job just one year later following an argument with another architect on the team, but the basilica’s evolution is still continuing to this day, meaning this modern wonder has been a work in progress for over 140 years.

La Sagrada Familia is due to be completed in 2026, meaning that it will have taken longer to build than the Egyptian pyramids. The original purpose of the building was to encourage Christianity in Barcelona at a time when the religion was in decline there. When Antoni Gaudi took over as chief architect in 1883, a new style was proposed. Gaudi’s signature style included geometric patterns and biomimicry – shapes largely inspired by nature. These elements can be seen in fine detail throughout La Sagrada Familia, such as the branching columns creating a forest-like theme in the central church area.

3 SPILLWAY INLET To prevent flooding, any overflowing water enters spillways eight metres below the dam’s top. 2 5 POWERHOUSE Water passes through turbines at speeds of 85 miles per hour. A generator turns this kinetic energy into electricity. 2 INTAKE TOWERS These four concrete structures control the water supply that reaches the power plant turbines. 3 1 5 1 DAM Over 3,300,000 cubic metres of concrete makes up the dam. 4 6 VALVE HOUSES These components are built about 55 metres above the river level to monitor the release of water through outlets. 6 4 PENSTOCKS Water travels through steel pipes known as penstocks to the powerhouse.

The dam is named after US President Herbert Hoover, who provided funds for construction

4.5 million people visit the building each year, despite it still being incomplete