Himmler had an abiding interest in the past, and in how it could provide a blueprint for the future. However, his views of the ancient Germanic peoples differed from Hitler's in certain areas. Hitler was perplexed as to why ancient societies in southern Europe had developed more advanced technology and architecture than their contemporaries in northern Europe. Hitler stated that "People make a tremendous fuss about the excavations carried out in districts inhabited by our forebears of the pre-Christian era. I am afraid that I cannot share their enthusiasm, for I cannot help remembering that, while our ancestors were making these vessels out of stone and clay, over which our archaeologists rave, the Greeks had already built the Acropolis." Hitler explained this by claiming that the Aryans must also have inhabited the south of the continent and that they were responsible for establishing the societies of ancient Greece and Rome. Specifically, he believed that it was the warmer climates of the south that enabled these Aryans to develop in ways that those living further north, in colder and wetter climates, did not. Himmler was aware of these views but, unlike Hitler, admired what he believed was the fierceness and valour of the Germanic tribes of northern Europe. He was particularly interested in Tacitus's "Germania", an ethnographic and historical account of the Iron-Age Germanic tribes written by the Roman historian at the end of the first century CE.