from the Italian side and from the Swiss side, with a margin of error of 0.1 m. Monte Rosa succeeded the Finsteraarhorn as the highest summit of Switzerland in 1815, when Valais joined the Swiss Confederation. Though the Mediterranean can hardly be visible from the summit of Monte Rosa because of intervening mountains, the view to the south extends to the Apennines, the mountains of Corsica and the Maritime Alps. On the north side the view extends to the Jura and further to the Vosges, the Swiss Plateau being mostly hidden by the high range of the Bernese Alps. History Early exploration Monte Rosa could be seen from many places on the south side of the Alps and it had been mentioned in many travel diaries. At the end of the 15th century some outlines of the mountain may possibly have been painted by Leonardo da Vinci into the background of the Madonna of the Rocks or other pictures. Da Vinci explored the Italian side of the mountain and made some observations, though there is but scanty evidence that he had climbed even a minor summit in the neighbourhood. He was intrigued by the permanent snow lying on the mountain and the darkness of the sky above him, he wrote: "The base of this mountain gives birth to the 4 rivers which flow in four different directions through the whole of Europe. And no mountain has its base at so great a height as this, which lifts itself above almost all the clouds; and snow seldom falls there, but only hail in the summer, when the clouds are highest. And this hail lies [unmelted] there, so that if it were not for the absorption of the rising and falling clouds, which does not happen more than twice in an age, an enormous mass of ice would be piled up there by the layers of hail, and in the middle of July I found it very considerable; and I saw the sky above me quite dark, and the sun as it fell on the mountain was far brighter here than in the plains below, because a smaller extent of atmosphere lay between the summit of the mountain and the sun." At the end of the eighteenth century, the people of the Italian valleys believed that a lost valley existed, hidden away between the glaciers of the great chain. The discovery of