Historians have linked obelisks to the Egyptian gods and sunlight, particularly Ra, who was the greatest of the pantheon and subsequently had the largest cult. Pharaohs had authority because they claimed to be direct descendants from Ra (later, Horus). You don't disobey someone who is considered a god on Earth unless you want to spend the rest of your life as a slave, y'know? They were buried in tombs and pyramids with special preparations done (organs removed, belongings stored, etc.) because the royals believed in life after death. Morrison's stated more than once that he sees superheroes as the new gods. The Al Ghuls view themselves as part of a dynasty; they are destined to rule the world, politics and free will be damned. Sounds familiar. So what does all this mean for the story? [BLACKOUT]The empty graves suggest eventual resurrection for Talia and Damian, a common theme both in modern superhero comics and ancient Egypt's mythology.[/BLACKOUT]
The gravestones are frozen rays of sunlight in a bleak, dark, grim thunderstorm. Semiotics!