In rude and unsettled times, such insular sites afforded safe retreats, all communication with the mainland being cut off, except by boats, or by such wooden bridges as could be easily removed. The Swiss lake-dwellings seem first to have attracted attention during the dry winter of 1853-54, when the lakes and rivers sank lower than had ever been previously known, and when the inhabitants of Meilen, on the Lake of Zurich, resolved to raise the level of some ground and turn it into land, by throwing mud upon it obtained by dredging in the adjoining shallow water. During these dredging operations they discovered a number of wooden piles deeply driven into the bed of the lake, and among them a great many hammers, axes, celts, and other instruments. All these belonged to the stone period with two exceptions, namely, an armlet of thin brass wire, and a small bronze hatchet. Fragments of rude pottery fashioned by the hand were abundant, also masses of charred wood, supposed to have formed parts of the platform on which the wooden cabins were built. Of this burnt timber, on this and other sites, subsequently explored, there was such an abundance as to lead to the conclusion that many of the settlements must have perished by fire. Herodotus has recorded that the Paeonians, above alluded to, preserved their independence during the Persian invasion, and defied the attacks of Darius by aid of the peculiar position of their dwellings. "But their safety," observes Mr. Wylie,* "was probably owing to their living in the middle of the lake, (Greek) en mese te limne, whereas the ancient Swiss settlers were compelled by the rapidly increasing depth of the water near the margins of their lakes to construct their habitations at a short distance from the shore, within easy bowshot of the land, and therefore not out of reach of fiery projectiles, against which thatched roofs and wooden walls could present but a poor defence." (* W.M. Wylie "Archaeologia" volume 38 1859, a valuable paper on the Swiss and Irish lake-habitations.) To these circumstances and to accidental fires we are probably indebted for the frequent preservation, in the mud around the site of the old settlements, of the most precious tools and works of art, such as would never have been thrown into the Danish "kitchen-middens," which have been aptly compared to a modern dusthole. Dr. Ferdinand Keller of Zurich has drawn up a series of most instructive memoirs, illustrated with well-executed plates, of the treasures in stone, bronze, and bone brought to light in these subaqueous repositories, and has given an ideal restoration of part of one of the old villages (see Plate 1 above),* such as he conceives may have existed on the lakes of Zurich and Bienne.