Fort Mifflin

Fort Mifflin is a historic fortification on Mud Island in the Delaware River, approximately five miles south of central Philadelphia. Originally constructed by the British in 1771 as part of Philadelphia's harbor defenses, the fort was seized by American forces at the outbreak of the Revolution and played a crucial role in delaying the British capture of Philadelphia in autumn 1777. The garrison's heroic resistance during a five-week siege (September 26 to November 15, 1777) bought precious time for the Continental Army and Congress to evacuate and for supplies to be removed from the city. Though the fort ultimately fell, its defenders demonstrated the determination that would sustain the revolutionary cause through years of struggle. Fort Mifflin continued to serve military purposes through the Civil War and both World Wars before being designated a National Historic Landmark in 1970. Today the fort is operated by the city of Philadelphia and is open to visitors as one of the most intact Revolutionary War fortifications in the country.

Colonial Construction

The British recognized the strategic importance of controlling the Delaware River approaches to Philadelphia and began constructing fortifications on Mud Island in 1771. The site, a low marshy island approximately 200 yards from the Pennsylvania shore, commanded the main shipping channel and could subject passing vessels to cannon fire. The British built an earthwork fort with wooden palisades and mounted cannon to protect Philadelphia from naval attack. The fort remained incomplete when the American Revolution began, and British forces abandoned it as Pennsylvania patriots took control of the colony's military resources. American engineers, including Polish volunteer Thaddeus Kosciuszko, strengthened and expanded the defenses in preparation for the conflict to come.

The American defensive system on the Delaware combined Fort Mifflin with Fort Mercer on the New Jersey shore and an extensive network of underwater obstructions called chevaux-de-frise—sharpened logs anchored to the river bottom to tear the hulls of ships attempting to pass. The Pennsylvania State Navy, a force of armed galleys and floating batteries, provided mobile firepower to supplement the fixed defenses. Together, these elements created a formidable barrier that any British force approaching Philadelphia by water would have to overcome. The strength of the Delaware defenses would be tested severely in the fall of 1777.

The 1777 Siege

When British General William Howe captured Philadelphia in September 1777, he faced a critical problem: his army occupied the city, but the Delaware River defenses prevented British ships from bringing supplies and reinforcements upriver. Howe's army, dependent on supplies shipped from New York, could not sustain itself indefinitely without opening the river. The American forts and obstructions had to be reduced before British control of Philadelphia could be consolidated. Fort Mifflin, protecting the Pennsylvania side of the river, became the focus of an intense siege that would last over five weeks.

The British assault on Fort Mifflin combined naval bombardment with land-based artillery positioned on Province Island, just south of the fort. The defenders, numbering only a few hundred men under the command of Lieutenant Colonel Samuel Smith and later Major Simeon Thayer, faced overwhelming firepower. British warships, including ships of the line mounting 64 guns, bombarded the fort from the river while land batteries fired from close range. The wooden palisades and earthen walls provided inadequate protection against this concentrated bombardment. During the siege's final days, the British fired an estimated 10,000 cannonballs at the small fort, reducing much of it to rubble and inflicting severe casualties on the defenders.

The garrison's resistance was remarkable. Soldiers worked through the night to repair damage from each day's bombardment, rebuilding walls and remounting cannon under continuous fire. The wounded were evacuated across the river to Fort Mercer, while fresh troops were brought in to replace casualties. The garrison held out until November 15, 1777, when the surviving defenders—fewer than 200 able-bodied men—evacuated the ruins under cover of darkness, setting fire to what remained. The British had captured the fort, but the five-week delay had allowed Continental forces to secure supplies and establish the defensive position at Valley Forge. Fort Mercer fell a week later, and the Delaware was finally open to British shipping.

Later Military Use

Fort Mifflin was rebuilt after the Revolution and continued to serve as a military installation for over 150 years. The current stone fortification, designed by French military engineer Pierre Charles L'Enfant (later famous for planning Washington, D.C.), was constructed between 1798 and 1803 as part of a national system of coastal defenses. The fort saw no combat during the War of 1812 but was expanded and modernized in subsequent decades. During the Civil War, Fort Mifflin served as a prison for Confederate soldiers and political prisoners, with conditions that drew criticism even from contemporaries accustomed to the harsh realities of wartime detention.

The fort remained an active military installation through both World Wars, serving various support and training functions for the Army and later the Navy. The end of military use came gradually, with the fort decommissioned in 1954 and transferred to the city of Philadelphia in 1962. The National Historic Landmark designation in 1970 recognized both the fort's Revolutionary War significance and the architectural importance of the early republic fortifications that survived later modifications. Today, Fort Mifflin encompasses approximately 49 acres and includes original structures from multiple periods of the fort's history, providing visitors with an unusually complete picture of American military architecture over two centuries.

Visiting Fort Mifflin

Fort Mifflin is open to the public from March through November, with tours offered on weekends and selected weekdays. The site includes the original moat, stone walls, and several buildings from the 1798-1803 reconstruction, as well as interpretive exhibits on the fort's history from the Revolution through the 20th century. Special events include Revolutionary War reenactments, Civil War commemorations, and ghost tours—the fort has a reputation as one of the most haunted sites in Philadelphia, with numerous reported paranormal experiences over the years. The combination of authentic Revolutionary War significance, well-preserved historic architecture, and atmospheric setting makes Fort Mifflin a distinctive destination for visitors interested in military history.

The fort is located on Fort Mifflin Road in Southwest Philadelphia, accessible by car though somewhat isolated from the city's main tourist areas. The setting along the Delaware River, now surrounded by industrial facilities and Philadelphia International Airport, offers a striking contrast between the 18th-century fortification and the modern infrastructure that has grown up around it. For those willing to make the journey, Fort Mifflin provides an opportunity to walk the grounds where American soldiers endured weeks of bombardment rather than surrender—a physical connection to the determination and sacrifice that made American independence possible.

See Also

• Battle of Brandywine
• British Occupation of Philadelphia
• Valley Forge
• Delaware River