Ishtar on arriving at the gate of the land of no return,
To the gatekeeper thus addressed herself:

“Gatekeeper, ho, open thy gate!
Open thy gate that I may enter!
If thou openest not the gate to let me enter,
I will break the door, I will wrench the lock,
I will smash the door-posts, I will force the doors.
I will bring up the dead to eat the living.
And the dead will outnumber the living.”

The above is from “The Descent of Ishtar Into the Underworld”. From the late bronze age ( c. 1300 BC or earlier ) in the Mesopotamia regions. From the earliest times we have the legend of the zombie. The undead rising and consuming the living. Something in the history of man triggered this legend. What event was that.