The underworld, over which Pluto reigned, was deep in the heart of the earth; but there were several entrances to it, one being near Lake Avernus, where the mist rising from the waters was so foul that no bird could fly over it. The lake itself was in an extinct volcano near Vesuvius. It was very deep, and was surrounded by high banks covered with a thick forest. The first descent into Hades could be easily accomplished (_facilis descensus Averno_, says the poet Virgil); but no mortal was daring enough to venture far into the black depths, lest he should never again see the light of day. At the portals of Hades sits the fierce three-headed dog Cerberus, who keeps all living things from entering the gate, and allows no spirit that has once been admitted to pass out again. From here a long dark pathway leads deeper into Hades, and is finally lost in the rivers that flow around Pluto's throne. The waters of the river Cocytus are salt, as they are made of the tears that stream forever from the eyes of those unhappy souls who are condemned to labor in Tartarus--that part of Hades that is the exclusive abode of the wicked. The Phlegethon River, which is always on fire, separates Tartarus from the rest of Hades, and wretched indeed is the soul that is forced to cross its seething waters. On the banks of the Acheron, a black and turbid river, stand the souls who come fresh from the sunlit earth; for all must pass this river and be brought before the judgment-throne of Pluto. There is no bridge over the murky stream, and the current is so swift that the boldest swimmer would not trust himself to its treacherous waters. The only way to cross is by the leaky, worm-eaten boat rowed by Charon, an aged ferryman who has plied his oar ever since the day that the curse of death first came upon the earth. No spirit is allowed to enter the leaky craft until he has first paid Charon the fee of a small coin called the obolus. (During the funeral services, before the body is committed for burial, this coin is laid on the tongue of the dead, that the soul may have no trouble in passing to the throne of Pluto.) If any spirits cannot furnish the necessary money, they are ruthlessly pushed aside by the mercenary boatman and are required to wait a hundred years. At the end of this time Charon grudgingly ferries them over the river free of charge. As the unstable boat can hold but few, there is always an eager group of spirits on the further bank, clamoring to be taken across the river; but Charon is never in a hurry, and repulses, sometimes with his oar, the pitiful crowd that waits his grim pleasure.