1 - creative license ? the film adapts miller's graphic novel not the writings of herodotus
2 - the trailer contained a number of other, um, elaborations that have no historical basis.
3 - the director may be mixing myth with what we know from the historical record. he may be seeing thermopylae from the 'eyes of the spartans' thereby incorporating
their religious ideas to justify their destiny and mission.
4 - the 'hole' may be a pit to a dungeon, a labyrinth, or other subterranean area. theseus walks through one such place to reach and kill the minotaur.