Now these rivers are many, and mighty, and diverse, and there are four principal ones, of which the greatest and outermost is that called Oceanus, which flows round the earth in a circle; and in the opposite direction flows Acheron, which passes under the earth through desert places into the Acherusian lake: this is the lake to the shores of which the souls of the many go when they are dead, and after waiting an appointed time, which is to some a longer and to some a shorter time, they are sent back to be born again as animals. The third river passes out between the two, and near the place of outlet pours into a vast region of fire, and forms a lake larger than the Mediterranean Sea, boiling with water and mud; and proceeding muddy and turbid, and winding about the earth, comes, among other places, to the extremities of the Acherusian Lake, but mingles not with the waters of the lake, and after making many coils about the earth plunges into Tartarus at a deeper level. This is that Pyriphlegethon, as the stream is called, which throws up jets of fire in different parts of the earth. The fourth river goes out on the opposite side, and falls first of all into a wild and savage region, which is all of a dark-blue colour, like lapis lazuli; and this is that river which is called the Stygian river, and falls into and forms the Lake Styx, and after falling into the lake and receiving strange powers in the waters, passes under the earth, winding round in the opposite direction, and comes near the Acherusian lake from the opposite side to Pyriphlegethon. And the water of this river too mingles with no other, but flows round in a circle and falls into Tartarus over against Pyriphlegethon; and the name of the river, as the poets say, is Cocytus.