I like the atmosphere of that
Here’s a page all about it:
But tl;dr, it was made by a secret group to suppress any attempts to penetrate further north into Chernobyl, and anyone caught within it’s radius was rendered powerless and turned into mindless zombies.
We thank you, O Monolith, for revealing the cunning plan of your enemies to us. May your light shine down on the soldiers who gave their lives in service to your will. Onward, warriors of the Monolith, avenge your fallen brothers. Blessed as they are, in their eternal union with the Monolith. Bring death to those who spurned the holy power of the Monolith.