In the midst of summer, after long heat, the vapour rises, and is in a degree dissipated into the sky, and then by following devious ways an entrance may be effected, but always at the cost of illness.  If the explorer be unable to quit the spot before night, whether in summer or winter, his death is certain.  In the earlier times some bold and adventurous men did indeed succeed in getting a few jewels, but since then the marsh has become more dangerous, and its pestilent character, indeed, increases year by year, as the stagnant water penetrates deeper.  So that now for very many years no such attempts have been made.

The extent of these foul swamps is not known with certainty, but it is generally believed that they are, at the widest, twenty miles across, and that they reach in a winding line for nearly forty.  But the outside parts are much less fatal; it is only the interior which is avoided.

Towards the Lake the sand thrown up by the waves has long since formed a partial barrier between the sweet water and the stagnant, rising up to within a few feet of the surface.  This barrier is overgrown with flags and reeds, where it is shallow.  Here it is possible to sail along the sweet water within an arrow-shot of the swamp.  Nor, indeed, would the stagnant mingle with the sweet, as is evident at other parts of the swamp, where streams flow side by side with the dark or reddish water; and there are pools, upon one side of which the deer drink, while the other is not frequented even by rats.

The common people aver that demons reside in these swamps; and, indeed, at night fiery shapes are seen, which, to the ignorant, are sufficient confirmation of such tales.  The vapour, where it is most dense, takes fire, like the blue flame of spirits, and these flaming clouds float to and fro, and yet do not burn the reeds.  The superstitious trace in them the forms of demons and winged fiery serpents, and say that white spectres haunt the margin of the marsh after dusk.  In a lesser degree, the same thing has taken place with other ancient cities.  It is true that there are not always swamps, but the sites are uninhabitable because of the emanations from the ruins.  Therefore they are avoided.  Even the spot where a single house has been known to have existed, is avoided by the hunters in the woods.

They say when they are stricken with ague or fever, that they must have unwittingly slept on the site of an ancient habitation.  Nor can the ground be cultivated near the ancient towns, because it causes fever; and thus it is that, as I have already stated, the present places of the same name are often miles distant from the former locality.  No sooner does the plough or the spade turn up an ancient site than those who work there are attacked with illness.  And thus the cities of the old world, and their houses and habitations, are deserted and lost in the forest.  If the hunters, about to pitch their camp for the night, should stumble on so much as a crumbling brick or a fragment of hewn stone, they at once remove at least a bowshot away.