Aberllefenni quarry is the collective name of three slate quarries, Foel Grochan, Hen Gloddfa (also known as Hen Chwarel) and Ceunant Ddu, located in Cwm Hengae, just to the west of Aberllefenni, Gwynedd, North Wales. It was the longest continually operated slate mine in the world until its closure in 2003. Foel Grochan is the quarry on the north side of the valley, facing Ceunant Ddu and Hen Gloddfa on the south; all three were worked as a single concern throughout their history. Rock was mainly extracted underground, though all three quarries had open pits as well. History Aberllefenni quarry may have started operating as early as the 14th century. The earliest confirmed date is 1500 when the local house Plas Aberllefenni was roofed in slates from the mine. In the seventeenth century the Lloyd family owned the quarry, and it passed to the Campbell family in 1725. In 1806, John Davies gained control which passed to the executor of his estate, Pryce Jones, in 1824. It was Davies who first organised commercial quarrying at Aberllefenni around 1810. Although only 3 workers were employed in 1825, by 1854 the quarry was producing significant amounts of slate; that year the enormous "Alma" open chamber at the top of Foel Grochan was named after the Battle of the Alma. By 1850, the quarry was owned by Colonel Robert Davies Jones, and was trading under the name Aberllefenni Slate Quarries. In 1873, the quarry appointed Robert Hughes as manager, and he quickly modernised working practices there. He installed new machinery in the extended mill, powered by a large waterwheel. That year the quarry employed 180 men. By 1879, the quarry was employing 169 men and produced nearly 4700 tons of finished slate and slab. The number of employees peaked in 1890 at 190. Production fluctuated but was trending downwards during the 1890s and 1900s. In 1908, the number of employees fell below 100 and declined further to 71 in 1910. The First World War saw a downturn in production in the whole industry, including at Aberllefenni. After the war there was a short boom into the early 1920s, but then the price of slate began to fall. By the early 1930s, the industry was in a deep depression, with a 3-day week being worked for part of 1933. In 1935 the quarry was leased by Sir Henry Haydn Jones, owner of the Bryn