North of Abercynon, the Taff Valley contains one sight that’s hard to forget. Two neat lines of distant arches mark the graves of 144 people killed in October 1966 by an unsecured slag heap collapsing on Pantglas primary school in the village of Aberfan. Thousands of people still make the pilgrimage to the village graveyard, to stand silent and bemused by the enormity of the disaster. Among the dead were 116 children, who died huddled in panic at the beginning of their school day. A humbling and beautiful valediction can be seen on one of the gravestones, that of a 10-year-old boy, who, it simply records, “loved light, freedom and animals”. Official enquiries all told the sorry tale that this disaster was almost inevitable, given the cavalier approach to safety so often displayed by the coal bosses. Gwynfor Evans, then newly elected as the first Plaid Cymru (Welsh Nationalist) MP in Westminster, spoke with well-founded bitterness when he said: “Let us suppose that such a monstrous mountain had been built above Hampstead or Eton, where the children of the men of power and wealth are at school”. But that, of course, would never have happened.