Situated near Hengoed, in 1905 Powell Duffryn began the sinking of Penallta colliery, and had employed 291 men by 1908. The two shafts Nos.1 (downcast 783 yards (716 m)) and 2 (upcast 750 yards (690 m)), and at the time were the deepest in the South Wales Coalfield. The first coal was raised in 1909, with the railway served by the Cylla branch which connected it to both the Rhymney Railway from the Ystrad Mynach north junction, and the Newport, Abergavenny and Hereford Railway. By 1923 there were 2,395 men employed, producing from the Six Feet seam, and at peak production during the 1930s, there were in excess of 3,200 men employed. In 1930 it produced 975,603 tons, and in 1935 it held the European record for coal winding