One prominent feature in the history of these lake dwellers is their gradual advance in the arts of civilization. While the main features of their settlements remain very much the same during the whole period of their residence, there is a gradual improvement in the details; the settlements become larger, and the implements, etc., better finished. And this is especially observable in the change of material which the dweller uses. In the earlier stages of his existence stone is the predominant feature, all his knives, saws, chisels, axes, etc., are made from this substance; but as time rolls on, one or two implements are found made of bronze, which is a mixture of tin and copper, and requires for its production a certain amount of knowledge and mechanical skill. Gradually the number of bronze implements increases until eventually stone is superseded altogether, and improved forms of weapons of war make their appearance, and his work has a more finished look, arising from his improved implements. Whether the manufacture of bronze was an original discovery of his own, or whether it was an importation from some more advanced race, is not certainly known; but as he undoubtedly had intercourse with the East, it is probable that the first bronze was imported, and that afterward he discovered the way to manufacture it himself. However this may be, it seems evident that the introduction of this material greatly aided his development. As stone gave place to bronze, so in the course of time this latter gave place to iron, probably introduced in the same manner some considerable time before the dawn of history; and this metal held its place until these habitations were finally abandoned. With regard to the religion of these lake dwellers, if they had any, nothing is known. From some curious objects formed somewhat like the crescent of the moon, which are found in considerable numbers, it has been supposed that they worshiped that body; but there seems to be really no evidence for this supposition, and these objects may only have been ornaments, or perhaps charms, fixed above the doors of their huts something after the manner of the horse shoe nailed over the door in modern times to keep away evil spirits. So far as can be inferred from the remains that have been examined, the same race seems to have inhabited these dwellings from their commencement to their end. There is no appearance of invasion from without; all seems continuous. Probably his race came in early time from the East, and were a pastoral people, with flocks, herds, and domestic animals, and built their peculiar habitations to protect themselves from human enemies. Certainly the arrangements were well fitted for the purpose in those days, when the club and the spear were almost the only weapons of offense. Dr. Keller, who has investigated this subject with great care, is of the opinion that these lake dwellers were a branch of the great Celtic race.