There's nothing more moving than watching the changing of the guard at the Tomb of the Unknowns at Arlington Cemetery.

A tomb that's guarded 24 hours a day, 365 days a year, The Tomb of the Unknowns has interred the remains of unknown soldiers since WWI. And serving as a guard at such a prestigious and solemn site requires that a soldier possess a number of special attributes to be chosen for such an honor. And it's an honor that is not taken very lightly.

Here's a behind-the-scenes perspective as soldiers prepare for their chosen duty: