This is still more remarkable in such Places, as not only are Situated in the forementioned Climate, but are likewise deprived of a constant Succession of pure and clear Air. An Instance of this we have in _Grand Caire_, which besides being subject to the common Disadvantages of the Country, (as are a Climate hot and scorching, a Situation low and flat, exposed chiefly to the warm Winds, their Water fetid and stagnating, being reserv'd in Vaults and Canals, which are Annually fill'd by the Overflowing of the River, the Air abounding with putrid Steams and Exhalations, arising from the Parts of Animals, Vegetables, and other Substances brought down and there deposited by the River), lies close under the Hill of the Castle, by which all Wind and Air is intercepted, which causes such a stifling Heat there, as ingenders many Diseases.[d] [d] _Therenot_'s Travels, Part. 1. pag. 128. That these may justly be esteem'd the Causes of the greater Frequency of these Diseases in this Place, than others in the same Climate, appears from their being so rarely known in those Places, which tho' equally hot, enjoy an Air free from Vapours.[e] Thus in _Numidia_ and some other Parts of _Africa_, the Plague is scarce to be found once in a hundred Years, and hardly at all in the Land of _Negroe_.[f] [e] _Piso_ Hist. _Ind._ & _Brasil_. [f] _Purchas_ Pilgrim. lib. 6. cap. 13. [Sidenote: _Several Causes of the Plague._] The other Observations of the Causes of these Fevers, may be reduced to such as arise from the Stinks of stagnating Waters in hot and close Weather, to some putrid Exhalations of the Earth, to the Parts of Animals and Vegetables putrifying in the open Air, or the taking of corrupt & unwholsome Nourishment. Of the first kind was that at _Selinis_, occasioned by the stinking Exhalations of the stagnating Waters adjacent, which the discerning _Empedocles_ removed by scouring its Ditches from their Filth, by a fresh Current of Water drawn from two Rivers in the neighbouring Country[g]. [g] _Plutarchi_ Lib. [Greek: peri polypragmosynês]. To the second Class may be reduced that Pestilential Fever, which the same great Philosopher check'd at _Agrigentum_, by stopping the Mouths of some neighbouring Mountains, whose pernicious Fumes had infected the adjacent Country[h]; As also that mentioned by _Ammianus_ _Marcellinus_, which broke out in _Seleucia_, and over-ran a great Part of _Greece_, _Italy_, and _Parthia_, and took its Rise from the opening of an old Vault in the Temple of _Apollo_. [h] _Diog. Laert._ in Vit. Emped.