On September 11, 2023 a once- in-a-thousand-year storm dumped an unprecedented level of rainfall across eastern Libya.

It rapidly filled up the reservoirs behind two dams placed along a seasonal river that led into the Libyan city of Derna, which at that time had a population of around 90,000 people.

One after the other, the enormous water loads placed on each of the dams proved too much for them to bear, leading to their catastrophic failures, which send a titanic surge of water tumbling down through the valley directly toward the city as if it were a tsunami.

Coming from inland at about 3am with little to no warning, the water crashed into the city as it was sleeping with apocalyptic results.

As much as one quarter of the city of Durna was obliterated within minutes, entire city blocks and buildings were annihilated and swept up by the surge out into the sea as many as 24,000 people who lived in the city were killed, easily making it the deadliest dam collapse disaster of the entire 21st century and among the deadliest in human history.

Here’s how it all happened and why it all went so horribly wrong.