The Green Bridge
The Green Bridge of Wales is one of the most spectacular natural rock arches in the British Isles, and almost certainly the finest of its kind in Wales. Located on the Pembrokeshire coast near Castlemartin, it stands as a masterpiece of coastal geology — a massive limestone promontory that has been sculpted over millennia by the relentless action of the sea into a soaring natural arch. The bridge spans the churning waters of the Bristol Channel, its creamy grey limestone rising dramatically from the cliffs and framing a perfect window of sky and ocean beyond. It is a site of genuine awe, the kind of place that stops people in their tracks the moment it comes into view, and it forms one of the centrepieces of the Pembrokeshire Coast National Park, which was established in 1952 and remains the only coastal national park in Wales.
The formation of the Green Bridge is the result of processes that began hundreds of millions of years ago, when the region lay beneath a shallow tropical sea and the accumulated remains of marine organisms slowly compressed into the carboniferous limestone that defines this coastline today. Over many thousands of years following the last ice age, wave action exploited natural weaknesses and joints in the rock face, cutting sea caves into a headland from both sides simultaneously. Eventually the two caves met and broke through, leaving the arch standing as the surviving roof. The name "Green Bridge" is thought to refer to the green vegetation — mosses, grasses and sea pinks — that colonises the top of the arch and the surrounding cliff tops, softening the otherwise stark grey rock with a vivid living carpet. Over geological time the arch will inevitably collapse, as the sea continues to undercut its legs, but for now it stands in magnificent defiance of the ocean.
Standing at the cliff edge near the Green Bridge is an experience that engages all the senses at once. The sound is perhaps most immediately striking: a constant deep percussive booming as waves surge into the cave systems beneath the arch and compress the trapped air, followed by a rushing exhalation as the water retreats. In heavy weather this roaring fills the whole clifftop. The smell is strongly saline, carried on winds that can be fierce even on otherwise calm days. Visually, the arch itself is enormous up close — far larger than photographs tend to suggest — and the limestone is richly textured with fossils, fissures, and orange and grey lichen. Choughs, those scarlet-billed members of the crow family so closely associated with Welsh sea cliffs, can often be seen tumbling acrobatically in the updrafts nearby, and razorbills or guillemots may be spotted on the water far below.
The surrounding landscape is the wild and largely treeless Castlemartin Peninsula, a flat-topped limestone plateau grazed by sheep and cattle, and one of the most botanically rich grassland habitats in Wales. The coastline here is part of a stretch of cliffs that also includes Stack Rocks — also known as Elegug Stacks — which lie just to the east and host one of the largest seabird colonies in Wales during spring and summer, with puffins, razorbills, guillemots and kittiwakes nesting in extraordinary numbers on the sheer rock pillars. The village of Bosherston, a few miles to the east, is known for its famous lily ponds, a National Nature Reserve where white water lilies bloom across a series of artificial but now entirely naturalised freshwater lakes in early summer. Freshwater West, one of the finest beaches in Pembrokeshire, lies to the north of the peninsula.
Access to the Green Bridge is somewhat unusual compared to many UK coastal landmarks, due to the fact that much of the Castlemartin Peninsula is occupied by a Ministry of Defence artillery range — the Castlemartin Range — which has been operational since the Second World War. This means that the access road to the Green Bridge and Stack Rocks is frequently closed during live firing exercises, which take place throughout the year. Visitors must always check in advance whether the range is open; this information is posted on the MOD's Castlemartin Range website and is also available by telephone. Access is generally better on weekends and during certain holiday periods when firing is suspended, though this varies. When the range is open, visitors drive down a military access road to a designated car park, from which it is a short walk along the cliff path to the viewpoints above the arch.
The best time to visit for combining dramatic scenery with wildlife is late spring or early summer, from May through to early July, when the seabird colonies at Stack Rocks are at their noisiest and most active, the cliff top flowers including thrift, sea campion and kidney vetch are in full bloom, and the lily ponds at Bosherston are carpeted with white blooms. Winter visits offer a different kind of drama — storms can send spray surging over the cliffs and the arch sounds its deepest, most elemental note in heavy seas — but conditions can be dangerously exposed. Visitors should always stay well back from the cliff edge, which in places overhangs caverns below and can be unstable. Dogs should be kept on leads both for safety and to protect the ground-nesting birds on the clifftop grassland during the breeding season.