The Barry Railway got an Act in 1898 permitting the extension to cross the Senghenydd branch of the Rhymney Railway and then cross the Rhymney Valley itself, joining the Brecon and Merthyr line near Duffryn Isaf; the new line was miles in length and included even more prodigious engineering challenges, in particular the Llanbradach viaduct. This alone cost about half of the £500,000 expense of building the line. The viaduct was 2,400 feet long with eleven spans 125 feet above the valley floor. The Brecon and Merthyr Railway received financial help to enable it to double-track parts of its system.