to protect the tomb of qin

Actually, the warriors are not in the tomb. Rather they guard the approach to the tomb. They know where the tomb is but have yet to find a way to excavate it without damaging important artifacts. This first Emperor of China wanted to live forever both before he died as well as after. To that end, he drank massive doses of live prolonging fluids provided him by his physicians. Ironically, they contained lots of Mercury so he poisoned himself in the process and died much earlier than he might have otherwise. As for his afterlife, he was convinced he needed the army to protect him from the people he killed (or had killed) during his many wars so he would live on forever.

Thank you very much! :D