This has been answered before by /u/jasoncaspian :
A question: Wouldn't it be kind of hard to have made such an intricate tomb for someone who didn't spend years focusing on his death and spending $ on afterlife (example pharos). It just doesn't seem like a thing that was thought of. A poor kid getting a rich man's tomb.
Wouldn't it be more plausible for him to have something small and less amazing-looking than this tomb?