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
Ben Nevis ice climbing, and holds snow until quite late in the year; in a good year, routes may remain in winter condition until mid-spring. Most of the possible rock routes are also suitable as winter climbs, including the four main ridges; Tower Ridge, for example, is grade IV on the Scottish winter grading system, having been upgraded in 2009 by the Scottish Mountaineering Club after requests by the local Mountain Rescue Team, there being numerous benightments and incidents every winter season. Probably the most popular ice climb on Ben Nevis is "The Curtain" (IV,5) on the left side of the Càrn