On the morning of Tuesday 11 September, 2001 a plane crashed into one of the World Trade Centre's twin towers. Less than 20 minutes later a second plane hit the other and by the end of the day the world had changed forever.
20 years on from the deadliest terror attack in human history the world is still shaped by the decisions made in the aftermath.
Almost 3,000 people were killed as a result of the attack, and even now 20 years after the attack, roughly 40% of the remains have yet to be identified.
On Saturday, President Joe Biden will lead the tributes to those who died with a sombre wreath-laying ceremony and moments of silence, though he is not planning on making any major public remarks.
The US is still feeling the effects of the attack today demonstrated by the recent crisis in Afghanistan as the West's withdrawal from the country they invaded in response to 9/11 ended in disaster and the return of the Taliban.