Conrad Gessner was the first naturalist to ascend the mountains in the 16th century, to study them, writing that in the mountains he found the "theatre of the Lord". By the 19th century more naturalists began to arrive to explore, study and conquer the high peaks; they were followed by artists, writers and painters. Two men who first explored the regions of ice and snow were Horace-Bénédict de Saussure (1740–1799) in the Pennine Alps, and the Benedictine monk of Disentis Placidus a Spescha (1752–1833). Born in Geneva, Saussure was enamored with the mountains from an early age; he left a law career to become a naturalist and spent many years trekking through the Bernese Oberland, the Savoy, the Piedmont and Valais, studying the glaciers and the geology, as he became an early proponent of the theory of rock upheaval. Saussure, in 1787, was a member of the third ascent of Mont Blanc—today the summits of all the peaks have been climbed.