The Pharaoh Shishak builds the Well of Souls in the city of Tanis to hide the mystical swag he stole from Jerusalem. The Bible mentions Shishak, but his stealing of the Ark is a fabrication.

The Well of Souls is a space that makes no ecological sense if you think about it, but nonetheless forms one of the most potent symbols in the whole film. It's filled with snakes from wall to wall. Snakes that have no earthly business being there and that would probably starve to death if left sealed up in a tomb for thousands of years. But hey, this is God's house, and if he wants them there, then that's where they will go.

"Why?" you may ask. It probably has something to do with the fact that Indy hates and fears all things snakey. If he wants to take the Ark out of there, he's going to have to confront the thing he fears the most. That's classic Campbellian imagery: from the descent into the Well to Indy's final emergence from it (which, you might notice, looks suspiciously like giving birth). This is the Innermost Cave, the location where the hero confronts all of his inner darkness and emerges stronger from the wisdom he discovers. Spielberg and screenwriter Lawrence Kasdan simply came up with a cool way to embody it: in this case, a lost tomb tailor-made for an old tomb-raider like Indy.

Oh, just one more question: Why'd it have to be snakes?