Ben Nevis the summit only to find "fragments of earthen and glass ware, chicken bones, corks, and bits of paper". It was not until 1847 that Ben Nevis was confirmed by the Ordnance Survey as the highest mountain in Britain and Ireland, ahead of its rival Ben Macdhui. The summit observatory was built in the summer of 1883, and would remain in operation for 21 years. The first path to the summit was built at the same time as the observatory and was designed to allow ponies to carry up supplies, with a maximum gradient of one in five. The opening of
Lists of mountains and hills in the British Isles 119. However, since 2006, Welsh peak Moel Siabod's prominence was recalculated to 600 metres, and the list of P600s was expanded to 120. The British Isle P600s, contain 54 of the 282 Scottish Munros, and 10 of the 34 Non-Scottish Munros, which are also called ; these 64 British Isles mountains meet the designation of being above in height, and in prominence (e.g. "Super-Majors"). P600 is an important international mountain classification criterion, along with Ultras or P1500, prominence above . The Database of British and Irish Hills also recognises the P500 mountain classification, prominence above . The Marilyns are mountains