This series of caches are located at Pontymoile canal basin.
Bridge 51 is a footpath leading from the canal up to Station Road, Griffithstown.
Bridge 51a was built after Bridge 51 and is known as The Skew Bridge which used to carry the Eastern Valley (Newport-Blaenavon) Railway Line over the Monmouthshire-Brecon Canal. The line superseded the canal, and in 1879 GWR took it over from the Monmouthshire Canal & Railway Company. The line closed to passenger traffic in 1963 and to all traffic in 1980 when Big Pit in Blaenavon closed down. The wall on the right is a retaining wall for the line.
A skew bridge, or oblique arch, is one where the span does not cross the obstacle at right angles. It took a considerable amount of skill to cut masonry blocks for a skew bridge, but construction became much easier and cheaper in the 19th Century with the increased use of brick in bridge building. It would be logical to assume that the Skew Fields took their name from this bridge, “the Skew Bridge Fields”, but this isn’t confirmed.