Too Obscure For You?
Kavian is attempting to cross the invisible bridge on FF2 logic, in which you must walk across an invisible bridge to get to Cecil’s final weapon, the Crystal Sword. It was in the last dungeon, which was also made of crystal. The marbles reference is for Indiana Jones and the Last Crusade, where Dr. Jones spilled sand across an invisible bridge to make it appear. You can imagine the trouble he would have had if he’d decided to use marbles instead.