Below the Eulæus is Elymais,[589] upon the coast adjoining to Persis, and extending from the river Orates[590] to Charax, a distance of two hundred and forty miles. Its towns are Seleucia[591] and Socrate,[592] upon Mount Casyrus. The shore which lies in front of this district is, as we have already stated, rendered inaccessible by mud,[593] the rivers Brixa and Ortacea bringing down vast quantities of slime from the interior,—Elymais itself being so marshy that it is impossible to reach Persis that way, unless by going completely round: it is also greatly infested with serpents, which are brought down by the waters of these rivers. That part of it which is the most inaccessible of all, bears the name of Characene, from Charax,[594] the frontier city of the kingdoms of Arabia. Of this place we will now make mention, after first stating the opinions of M. Agrippa in relation to this subject. That author informs us that Media, Parthia, and Persis, are bounded on the east by the Indus, on the west by the Tigris, on the north by Taurus and Caucasus, and on the south by the Red Sea; that the length of these countries is thirteen hundred and twenty miles, and the breadth eight hundred and forty; and that, in addition to these, there is Mesopotamia, which, taken by itself, is bounded on the east by the Tigris, on the west by the Euphrates, on the north by the chain of Taurus, and on the south by the Persian Sea, being eight hundred miles in length, and three hundred and sixty in breadth.