The Great Dee Viaduct on the Shrewsbury and Chester Railway. The viaduct crosses the river Dee in the Vale of Llangollen. The impressive viaduct consists of 19 semicircular arches of 60 feet span, the height from the bed of the river to the top pier is 148 feet. The structure is built of stone, the first stone was laid on the 19th April 1846. The line was finally opened to the public on the 14th October 1848.