Wall of Serpents

Defender, Infect
And there came forth poisonous serpents also upon
the face of the land, and did poison many people. And
it came to pass that their flocks began to flee before the poisonous serpents, towards the land southward, which
was called by the Nephites Zarahemla..And it came
to pass that the Lord did cause the serpents that they
should pursue them no more, but that they should
hedge up the way that the people could not pass..
-Ether 9:31&33