The Aberfan disaster which killed 144 people 40 years ago, most of whom were children, was a defining moment in Welsh history, Wales's First Minister Rhodri Morgan said this week.
The Welsh Assembly held a two-minute silence on Wednesday to remember the 116 children and 28 adults who died when a coal tip collapsed on a school in Aberfan, near Merthyr Tydfil.
The village will hold memorial events this week to mark the anniversary of the tragedy with which it became synonymous.
Mr Morgan called on the people of Wales to remember those who died on October 21, 1966. He compared the impact of their deaths to that of the 911 terror attacks and President Kennedy's assassination in the United States.
He said: "Everyone remembers how they heard about Aberfan.
"I first heard about it on the lunchtime news that day and found it hard to make sense of the horror - the fact that a primary school had been buried, that so many children had died, and the scale of the rescue operation."
Pupils were just beginning lessons when a landslide of mud and coal debris rushed down a hill on to Pantglas junior school. The tip above the school, weakened by heavy rain, buried classrooms and engulfed nearby houses.
As the rescue attempt began, people in the surrounding area went to the disaster site to dig through the mud for survivors.
"This was the 1960s. Wales still had 100,000 miners and coal was king," Mr Morgan said.
"The National Coal Board was the great power in the land. Coal was so important that we all accepted, until Aberfan, that there was a price to pay."
He added: "Americans think of the assassination of JF Kennedy and also of 911, events which fundamentally changed the country.
"For Wales, our defining moment came 40 years ago."
He said that the disaster prompted a movement of environmental and economic renewal in Wales. Despite a long litany of tragedies underground, Wales never foresaw that coal could take the lives of its children.
"That was new, and terrible. Aberfan defined post-War Wales, as would no other event,"said Mr Morgan.