Pallas settled in St Petersburg, becoming a favourite of Catherine II and teaching natural history to the Grand Dukes Alexander and Constantine. He was provided with the plants collected by other naturalists to compile the "Flora Rossica" (1784–1815), a Russian flora, and started work on his "Zoographica Rosso-Asiatica" (1811–31), a zoography of Russia and Asia. He also published an account of Johann Anton Güldenstädt's travels in the Caucasus. The Empress bought Pallas's large natural history collection for 2,000 rubles, 500 more than his asking price, and allowed him to keep them for life. During this period, Pallas helped plan the Mulovsky expedition, which was cancelled in October 1787.