What was a major historical event that occurred but people don't really know what actually happened?

It could have happened at any time, but people have a general idea of what happened. But what really went on there, what is the magnitude what actually happened. This could be ancient or more modern events. What do you think people know a little bit about but have no idea how huge it was.<br><br><br>EDIT: I'll start since I posted the thread, The first time the atom bomb was tested people are told that scientists weren't really sure what would happen. It's widely believed that Oppenheimer and his team weren't really sure what would happen when it was tested. In reality they were almost positive that it would work, but they had no idea how big the explosion would be. The first test detonation was the trinity test, it was a 20 kiloton explosion. The Hiroshima bomb was 15 kilotons, the Nagasaki bomb was 20 kilotons, the trinity test was as big as a nuclear bomb dropped on an inhabited city. It was also 300 feet in the air, and on a tower. And it exploded a bit bigger than a Nagasaki. It's hard to grasp just how big it was, but it was as big as a bomb that had killed thousands of people, and it was 300 feet in the air in the middle of no where.