A mummified man, determined to be 5,000 years old, was discovered on a glacier at the Austrian–Italian border in 1991. By the 6th century BC, the Celtic La Tène culture was well established. Hannibal famously crossed the Alps with a herd of elephants, and the Romans had settlements in the region. In 1800 Napoleon crossed one of the mountain passes with an army of 40,000. The 18th and 19th centuries saw an influx of naturalists, writers, and artists, in particular the Romantics, followed by the golden age of alpinism as mountaineers began to ascend the peaks. In World War II, Adolf Hitler kept a base of operation in the Bavarian Alps throughout the war.