Fort Mifflin, originally called Fort Island Battery and also known as Mud Island Fort, was built in 1772 by the British to protect Philadelphia. At the start of the Revolutionary War, the Americans claimed the fort and completed construction. It is located near the Philadelphia International Airport. It is one of the only remaining revolutionary war battlefields intact, which was also utilized during the Civil War, WW1 and WW2. It is also considered one of the most terrifying places in Pennsylvania.