The Stanley Embankment (known locally as the Cob) is a railway, road and cycleway embankment that connects the Island of Anglesey and Holy Island, Wales. It carries both the North Wales Coast Line for trains, which runs from Crewe to Holyhead and the A5 road between London and Holyhead. The embankment was designed by, and its construction overseen by, Thomas Telford and was named after the Stanley family who were significant benefactors to the area.
Prior to its construction the fastest route to Holyhead from the island's mainland was via the old stone bridge at Four Mile Bridge. However, when the A5 road was being constructed between London and the Port of Holyhead a more direct route was needed. Construction was started in 1822 and completed only a year later and was a total of 1,170 metres long. As with most other embankments it was significantly wider at the base (35 metres) than at the top (10 metres). During its construction rubble and other raw building materials were dug out of the earth from the land on the Anglesey side of the divide. A workers hamlet was built around this artificial valley, a settlement which has since grown into a medium-sized village, still named Valley even though the dip has long since gone.
Although partly damaged in a storm in 1824 the embankment site was chosen in the 1840s to carry the new train line across the county, the North Wales Coast Line. This significantly widened the structure. When this was completed in 1848 a tall dividing wall had to be built between road and rail so the trains did not startle the horses on the road. It remained that major road route between the island for over 175 years when it was joined in 2001 by the newly constructed A55 (North Wales Expressway) which bypasses Valley to the south and runs close by Stanley Embankment. Although the A55 is faster and wider the two older routes are still used extensively and the railway line still runs along the original 1848 route.