The Green Bridge of Wales is one of the most famous landmarks in Wales, and one of the most spectacular sites on the Pembrokeshire Coast. It is located close to Castlemartin in the south of the county, and is adjacent to the Stack Rocks and the Cauldron.
The Green Bridge is a limestone arch. It is the limestone of the South Pembrokeshire Coast that is responsible for some of the most beautiful natural features. The arch formed when the sea wore away the rock underneath. Once the arch was a promontory of rock, jutting into the sea. It was solid, with no hole or arch to be seen. Weaknesses in the rock, known as joints and bedding planes, allowed the sea and the force of the waves to wear away the rock. At first, it is likely that a cave was formed in each side of the spur. As the sea gradually washed more rock away, the two caves joined together to make an arch.
One day in the future the centre of the arch will collapse, and the arch will become a stack.