Approximately 10,000 years ago The Durdle Door is the world's most famous stone arch. It was formed some 10,000 years ago when the sea penetrated through the Portland limestone. Looking west down the beach, solitary stacks out at sea indicate an older shoreline. Behind them lies a mysterious land that only archaeologists can explore. The Durdle Door isn't actually an door but a stone arch, which is a hole cut in one of the rocks large enough for a person to pass through. It's located near Bridport in Dorset, England. The arch stands on the site where millions of shells from all over the world were once collected by the Celts and brought to Europe for use as jewelry, or as food ingredients if used carefully. These days there are still shells available for sale under the label "Durdle Door shells." Although the arch is not exactly old it does provide evidence of human activity from about 9,500 years ago. Before this time, the coast at Bridport was much further away from the town itself. The raising of the level of the sea has exposed ancient soil layers filled with artifacts dating back to this earlier time. The arch was listed as an object of special scientific interest in 1951. This means that the arch is protected by law from certain types of development that might be necessary to maintain its status as an example of geological history.