"Only the most magnificent royal tombs would have side doors or alternative entrances built into them," Andrew said.

Kevin nodded. "That's exactly right. Royal burial grounds often took decades to complete. Emperor's tombs especially, would begin construction the day they took the throne. Some took up to 50 years to finish.

"Because of this, they inevitably had to create multiple side doors and alternative entrances. This made it convenient for craftsmen to come and go and allowed the empero