The Liberty Bell, in Philadelphia, Pennsylvania, is one of the most prominent symbols of the American Revolutionary War. It is a familiar symbol of independence within the United States and has been described as an icon of liberty and justice.
According to tradition, its most famous ringing occurred on July 8, 1776, to summon citizens of Philadelphia for the reading of the Declaration of Independence. Historians today consider this highly doubtful, as the steeple in which the bell was hung had deteriorated significantly by that time. The bell had also been rung to announce the opening of the First Continental Congress in 1774 and after the Battle of Lexington and Concord in 1775.
The Liberty Bell was known as the "Independence Bell" or the "Old Yankee's Bell" until 1837, when it was adopted by the American Anti-Slavery Society as a symbol of the abolitionist movement.
Source: http://en.wikipedia.org/wiki/Liberty_Bell
