It's from The Second Coming and decribes that mythological event. Everything is backwards from normality in the poem.
"Things fall apart; the centre cannot hold;
Mere anarchy is loosed upon the world,"
Taking it out of context changes it a lot.
Were vexed to nightmare by a rocking cradle,
And what rough beast, its hour come round at last,
Slouches towards Bethlehem to be born?
@LenHazell53 I haven't read that since college, which is a shame.