 As the expedition neared dangerous areas, he had to travel in a convoy with an escort.Physically Humboldt was in good condition, despite his advancing years, writing to Cancrin "I still walk very lightly on foot, nine to ten hours without resting, despite my age and my white hair".Between May and November 1829 he and the growing expedition traversed the wide expanse of the Russian empire from the Neva to the Yenisei, accomplishing in twenty-five weeks a distance of .