Cascata delle Marmore, or Marmore Falls, is a magnificent sight to behold. Water from the Velino River surges through the hills above the city of Rieti before bursting over verdant cliffs and plummeting into the valley below. The tiered waterway, surrounded by trees and greenery, looks like a fabulous force of nature.

In reality, there’s nothing natural about these falls. At 541 feet tall, this waterway is the tallest human-made waterfall in the world. It’s impressive stature is a 2,000-year-old testament to human engineering.

The Romans built Cascata delle Marmore in 271 BC. At the time, the hills were a marshy spot, full of stagnant water and disease-bearing insects. To fix the issue, a Roman consul ordered workers to construct a canal that would send the water soaring over a nearby cliff and down into the Nera River, which flowed through the valley below.

While this did in fact fix the swamp issue, it unfortunately created another problem. The canal was so effective at rerouting the water that it wound up flooding the river below, threatening the nearby city of Terni. Tension over water management between the highland and lowland residents became so heated the Roman senate was forced to intervene in 54 BC (though their involvement actually accomplished nothing).

The falls continued to flow uninterrupted until the 15th and 16th centuries, when a couple of new channels were created to help divert the flooding. Cascata delle Marmore received its current look in 1787, when an architect diverted some of the water to create a series of lateral cataracts.

Humans still control the waterfall. Much of the Velino River is now channeled into a hydroelectric plant, which reduces the fall’s thundering, roaring flow to a mere whimper. But twice a day, much to the delight of visitors, the power plant flips a switch and lets the water once again gush over the cliffs as it had for millennia.