Fort Mifflin (located right next to Philadelphia International Airport) was part of a defense team to keep the British from shipping supplies to their soldiers in Philadelphia. For six weeks the British fired on Fort Mifflin at the rate of 1,000 cannon balls an hour. It came to a close on November 16, 1777 when The Continental Army surrendered the fort. This Philadelphia hidden treasure was also heavily used during The Civil War. This weekend the fort remembers.