The Liberty Bell is a cultural icon of the United States of America.
The Liberty Bell was cast in 1752. Prior to the outbreak, the Liberty Bell had a place of honor at the Liberty Bell Center in Philadelphia, Pennsylvania.
After Philadelphia became overrun with zombies, government forces tried to save cultural icons of American history.
The Westward-bound survivor group found the Liberty Bell on a flat-bed truck surrounded by zombies. They killed the zombies and took the truck. After encountering more zombies, the Bell broke free of it's restraints and careened down a street, smashing zombies as it tumbled.
Doc was really impressed by the result, wishing to see that again.