The Liberty Bell was designed as the bell for the Pennsylvania State House in 1751. It was rung for many events, including the coronation of King George III in 1760. Among its most famous ringings was on July 8 1776 to announce the first public reading of the Declaration of Independence.
The first bell was made in England. It arrived in Philadelphia in 1752 and cracked upon its first test ringing. A second bell was cast but its tone was found to be unsatisfactory. A third bell was cast, hung in the Pennsylvania State House (now Liberty Hall) in 1753. It weighs over 2000 pounds and its composition is 70% copper, 25% tin, and small amounts of lead, zinc, arsenic, gold, and silver.  It was rung on every anniversary of Independence Day (4th of July) until the time it cracked when rung on July 8, 1835 at the funeral of U.S. Supreme Court Justice John Marshall.
- "Proclaim Liberty throughout the land unto all the inhabitants thereof." (Leviticus 25:10)
The Liberty Bell is an important patriotic symbol and it's image can be found on many things including the reverse side of the Benjamin Franklin half-dollar coin issued by the United States Mint between 1948 and 1963.  
The United States Postal Service features an image of the Liberty Bell on the "Forever stamp" which debuted on April 12, 2007. The stamp cost 41 cents and the Postal Service promises it will always be accepted as postage for First Class letters weighing 1 ounce or less anytime in the future regardless of price changes. 
- The Liberty Bell - Setting the Stage The National Park Service
- The Liberty Bell The National Park Service