4. Pass on to the men who raised the tumuli and we find still further signs of progress. Of these the tumuli themselves are the most significant. For in them we see the beginning of the art of building. I do not say that houses were unknown to the kitchen-midden men; only that we have no proof that they lived in houses; and we are here taking the evidences of advancing civilization as we come across them. In the case of the still earlier cave-dwellers we may take it for granted that the art of house-building was unknown to them, and quite as much so to the men of the river drift.[16] True, the tumuli are not houses; they are tombs. But the men who could raise these tombs could raise houses likewise, and there can be little doubt that the architecture of the tombs, here and throughout the history of mankind, was modelled upon the architecture of the houses. Wherefore we may assume that these last were low and narrow chambers, a sort of constructed caves, so to speak, which is just what we should expect the earliest houses to be. We should expect that the first advance from cave-dwelling or burrowing in the ground would be to raise an artificial mountain and burrow within that. But soon the insecurity of this house would become apparent, and the next advance--no mean one, however,--would be the propping of stones upon others to make a chamber before the earth was heaped up in the tumulus, and when that step had been reached the art of house-building had begun. We might call the next step forward the acquisition of a religion, of which the first signs are apparent in the cromlechs of this age. In this case, again, we only follow the testimony of the remains that have been discovered in the order in which they have come to light. It would be far too much to say that the earlier stone-age men were without religious observances. All we can say is, that the first certain remains of these belong to the time of the tumuli and the cromlechs. The reasons which lead us to believe that these last, the cromlechs, had a religious character have been already given. Commerce was not unknown even to the cave-dwellers, but the first proofs of anything like a distant commerce come to us from the date of the grave-mounds. The domestic animals of the tumuli begin to be numerous--oxen, pigs, goats, and geese,--though these remains are not found in the earliest mounds. And there is likewise among them some trace of agriculture. Finally, traces of the art of pottery-making appear for the first time in these graves. * * * * * 5. The village communities show an advance to the most undoubted use of agriculture, to the planting of fruit-trees, to the weaving of cloths, and a much more extended practice of domestication than obtained among the men of the grave-mounds.