The Albion Steam Coal Company began work at Ynyscaedudwg Farm in 1884, one mile north of Pontypridd in a narrow valley along the road that today is the A470 to Llandudno. Two shafts went down, nineteen feet wide, set thirty-three yards apart, sunk to a depth of 646 yards through layers of rock and water until they reached the seam. By August 1887 the cages were running. The valleys above and below filled in around them - terraces of mortared stone climbing the hillsides, chapel and pub and corner shop, all of it built on the assumption that the pit would keep working. Two miners died sinking the shafts in March 1886. Four more died in November of that year as production began. By the time the seams were producing properly, the colliery had already taken its first six lives, and no one in Cilfynydd thought that was unusual.

The miners cut the coal by hand with picks, lying on their sides in seams two or three feet high, breathing dust thick enough to taste. The price of the work was paid in the body. Crushed fingers, broken spines, ribs that healed crooked from the bent-over labour. Black spit, and after a few years the slow drowning that miners called the dust - silicosis, pneumoconiosis, conditions for which there was no treatment and no compensation. Wages were thin; the profits went up the hill to landowners and shareholders. Joining a union was a sackable offence, and being sacked at one Welsh pit meant being blacklisted at every other within walking distance. Pit ponies, by contrast, were valued and looked after. A horse cost money to replace. A man, the owners reasoned, was already standing in line for the job.

The 23 June shift was a Saturday afternoon shift - newly introduced and, as the inquiry would later determine, fatally rushed. There was no time between shifts to clear or dampen the dust. The men were repairing roadways and clearing the working faces when the explosion came. The cause, traced by barrister J Roskill in his September report to the Home Secretary, was the deliberate blasting of timber props that had ignited a small pocket of gas. The gas ignited the coal dust hanging in the air, and the dust ignited the dust beyond it, and so the fireball travelled. By the time it stopped travelling, almost everyone underground was dead. The bodies came up to a temporary morgue improvised in the colliery's stable hayloft. Many were so badly burned and crushed that families could not be sure whose son or husband they were taking home. In several houses in Cilfynydd, mourners washed and laid out a body and only later discovered that it belonged to another household. Eleven men were never identified at all. A memorial to them stands at St Mabon's Church in Llanfabon, names absent, their grave their own.

The colliery was reopened within two weeks. The inquest, held at Pontypridd that August, dragged on for nine days as owners, inspectors and witnesses argued over what had ignited what. The jury was sure the gas had been accelerated by coal dust but could not agree on the spark. They were sure of one other thing: that the under-manager had neglected his duties by allowing shotfiring to continue against the rules. Roskill's report agreed and went further. Watering had been inadequate; the new Saturday shift had eliminated the safety gap between shifts; the practice of blasting timber was reckless. He recommended prosecuting the Albion Coal Company. The eventual outcome was a ten-pound fine against manager Phillip Jones and a two-pound fine against chargeman William Anstes. Two hundred and ninety dead; twelve pounds. One of the few survivors, a man named George Bamford, gave testimony from his hospital bed.

Albion kept working. By 1908 there were 2,589 men on the books; production peaked at 325,000 tons in 1934. The Albion Company went into liquidation in 1928, the assets bought by Powell Duffryn, the workings nationalised after the war into the National Coal Board in 1947. Penrhiwceiber was added to the production group and combined output climbed past 620,000 tons. The mine closed in September 1966, eighty years after the first shaft went down. The colliery yard is now Pontypridd High School - and on the 120th anniversary of the explosion the pupils made a film recreating it, putting themselves in the place of the boys who never came home. Two hundred and ninety men and boys lie scattered in graveyards across the valley, in the careful Welsh way of remembering by name. Cilfynydd is a small place. There is barely a chapel in it that does not carry one of those names on a wall.