There are several reasons. First, much evidence of prehistoric civilization is found in caves because the natural shelter helps preserve artifacts. The earliest cave dwellers date to the Paleolithic period, around 2.5 million years ago, and evidence suggests that these ancient nomads used caves as temporary shelters during their seasonal wanderings. The caves often lay on valley slopes and provided excellent views of animal migration routes. But there is no evidence that Stone Age peoples set up shop in caves for very long. Even Neanderthals, who lived in relatively cold regions of ancient Europe, used caves only for temporary shelter. Our more immediate ancestors did, of course, eventually move indoors. But permanent dwellings came about only with the invention of agriculture and animal husbandry. Before those world-changing inventions, prehistoric people were forced to follow their food away from the warmth and shelter of the cave.