On Friday, October 21, 1966, coal tips from Merthyr Vale Colliery slid down the mountainside and engulfed Pantglas School, 20 homes and a farm in the village. Water had accumulated in a stream beneath the tip, triggering the collapse.
Of the 144 who died, 116 were children, the majority aged between seven and 10. Roughly half the pupils at Pantglas School were killed, together with five of their teachers.
It was the final day of term before the half-term holiday.
The disaster remains one of the most devastating events in modern Welsh history. After leaving the Memorial Garden, the King, Queen and Prince of Wales walked to the Aberfan and Merthyr Vale Community Centre, greeting local residents along the way.