It’s 20 years since a clear, sunny morning in downtown Manhattan was transformed at 8:46am.

Four planes were hijacked on the east coast of the USA: two hit the World Trade Center. One hit the Pentagon, the heart of the country’s defence. Another went down in western Pennsylvania. It was a day that left nearly 3,000 dead.

It was a day that changed everything: from the way we live and travel and the threats we fear, to the global world order and modern terrorism. All of which still lives on today, from New York City to Kabul.

In today’s episode, Jon Snow takes us back to that fateful, generation-defining day, and recounts his visit to Ground Zero in November 2001. And a warning: this content contains distressing themes.