I was playing Dwarf Fortress, trying to make a pit for the garbage disposal, when I wondered if there were any historical accounts regarding such 'bottomless' pits as depicted in, for example, the movie '300'?
That scene, as dramatized as it sounds, is actually rooted in actual history and fairly accurate as far as movies go. Herodotus, on his Persian War writings, records that when Xerxes sent diplomats who demanded the symbolic tokens of submission/surrender ("earth and water") from Sparta, the Spartans threw them into a newly-dug well, laconically suggesting the Persian diplomats would find plenty of both at the bottom.
While not a bottomless pit per se, in the Tale/Saga of Ragnar Lothbrok (Ragnars saga Loðbrókar), Ragnar is recorded as being thrown into a pit full of snakes by King Ælla of Northumbria, where he met his demise. His prophetic last words were said to be "How the little piglets will grunt, when they learn of how the old boar suffered." This event is said to be the trigger for the Great Heathen/Viking Invasion of England.
Not an answer to your prime question but there's often confusion about what the pit is in '300'. It's actually a water well, you can see the bucket and rope in the background