Asturias was inhabited, first by "Homo erectus", then by Neanderthals. Since the Lower Paleolithic era, and during the Upper Paleolithic, Asturias was characterized by cave paintings in the eastern part of the area. In the Mesolithic period, a native culture developed, that of the "Asturiense", and later, with the introduction of the Bronze Age, megaliths and tumuli were constructed. In the Iron Age, the territory came under the cultural influence of the Celts; the local Celtic peoples, known as the Astures, were composed of tribes such as the "Luggones", the "Pesicos", and others, who populated the entire area with "castros" (fortified hill-towns). Today the Astur Celtic influence persists in place names, such as those of rivers and mountains.