The art in the Hermitage represents, for the most part, the former imperial collection of the tsars, which began some 300 years ago when Peter the Great began acquiring pictures and artefacts. It was hugely augmented in the late 18th century by Catherine the Great who bought many of the key Renaissance paintings. Nicholas I opened the collection as a museum in 1852, but it only became a state museum, with access to all, after the 1917 revolution. During the Soviet era, some works were sold, but the collection was also strengthened as many more works were looted first from rich Russians and later from occupied Germany. Most of the Impressionist and modernist art was amassed after the Revolution and came principally from the collections of Ivan Morozov and Sergei Shchukin – two great Russian patrons in the years running up to the First World War. These paintings, once on the top floor of the main museum, are now on display in the new galleries of the General Staff building, on the other side of Palace Square.