The Prince of Wales and the Duchess of Cornwall have laid a wreath in memory of Welsh miners killed in the collieries saying the country owes them "a debt of gratitude".
Charles and Camilla attended the Welsh National Miners Memorial in Senghenydd, in the Aber Valley, meeting relatives of those killed in the area's biggest disaster.
In 1913, the village's colliery was rocked by a huge underground explosion claiming the lives of 439 miners and one rescuer.
Roy Noble, patron of the village's heritage committee, welcomed the couple to the monument's "hallowed ground" which also commemorates a similar disaster from 1901.
Charles and Camilla were shown tiles inlaid around the sculpted bronze memorial, each bearing the names of the victims, some as young as 14.
As both intently studied those names, many from the same families, the Aber Valley Male Voice Choir sang the song Senghenydd, which asks "where have all the young men gone?", concluding "we will remember them".
Among the choir 70-year-old Viv Pitten, who lives at the top of the valley, said the disaster was "still raw" for the people of his generation.
Later, as Charles toured the village's Heritage Museum, he hailed the courage of the miners, and to those who paid the ultimate price digging the vital coal that helped drive Britain's industry.
He said: "My wife and I have so enjoyed this opportunity to meet you all and if I may say so to have a chance to pay our respects at the memorial.
"We just wanted to take this opportunity to congratulate all those who've been involved in ensuring such a marvellous memorial is there in memory of all those many people who died so tragically, not only in 1913, but in 1901.
"And in the fact you are commemorating so many other mining disasters which have afflicted so many other communities in this remarkable part of South Wales.
"I think we owe such an enormous debt of gratitude, respect and appreciation to those people - so many from the same families - who went underground and were courageous and determined enough to do so.
"Both of us are enormously proud to have this opportunity to be here."
Charles and Camilla, who had been due to visit the memorial's unveiling on the centenary of the disaster in October last year, spent a long time greeting crowds of villagers and taking posies of flowers presented by dozens of schoolchildren.
The couple met mother Helen Manship, and shared a playful moment with her one-year-old daughter Evie-Rae Manship, who seemed thoroughly bemused by the royal attention.
Mrs Manship said Charles seemed in good spirits.
She said: "I told him I was a mum of three, and he said 'you've got your hands full then' and then joked 'have they got permission to be off school?'"
Hilary Barbrook, 74, lost two grandfathers in the 1913 disaster.
She said: "They brought my one grandfather Hopkins James up, and he's buried in the nearby cemetery.
"My other grandfather Charles Brown, they couldn't find his body.
"Then 15 months after the explosion, they opened up that part of the mine and they found him and he was only recognisable from a ring he had on."
Ms Barbrook, who now lives in Caerphilly at the bottom of the valley, said it was still "very emotional".
She welcomed the royal visit and said: "I think it's very important for the recognition of what we've tried to do for all of Wales."
Charles and Camilla are four days into a five-day tour of Wales.
Camilla later visited Usk, celebrating the 50th anniversary of Royal Horticultural Society's Britain in Bloom competition and meeting local schoolchildren and community members.
Separately, Charles was being shown around a 15th century Welsh farmhouse which is being restored by the Landmark Trust, of which the Prince is a patron.
He continued on to Crickhowell in Brecon Beacons National Park in Powys, to view the production process for family-run organic apple juice maker Welsh Farmhouse.
He also dropped in to MT Cashell and Family Butchers, which has been run by Michael Cashell for 40 years.
Speaking afterwards, Mr Cashell said the royal visit was good for Crickhowell adding it "puts us on the map".
Paula Bonner, who was shopping in the butchers at the time, told Charles she was from London but went to the store as it does the "best back bacon".
"That's what I call a discerning customer," said Charles.