Fort Breendonk is a fortification built in 1906 as part of the second ring of defenses of the Réduit national around the city of Antwerp, Belgium. Originally one in a chain of fortresses constructed to defend Belgium against a German attack, Breendonk was near the town of the same name, about 12 miles southwest of Antwerp. It was covered by a five metre thick layer of soil for defense against bombings, a water-filled moat and measured 656 by 984 feet. The fort was used as a prison camp by the German occupiers during World War II. Today, the site is a national memorial (Nationaal Gedenkteken Fort van Breendonk in Dutch) and can be visited.

Belgium was invaded in August 1914 by the German army after refusing its request of unhindered passage to northern France.

The invasion began on August 4, 1914. Eager to reach Paris as soon as possible, the German army concentrated all its efforts towards the south, ignoring Antwerp.

Continued Belgian resistance from the north forced German command to attack Antwerp. On September 9, General Beseler was ordered to attack Antwerp. Siege artillery was sent north, having precipitated the fall of Namur and Maubeuge.

Breendonk is a small town in Belgium, population 3,000, halfway between Brussels and Antwerp.

Its name stems from the medieval Bredene Dunc which translates as "wide mound" or "a dry spot in the marshes."

In the 19th century it was known for its beautiful Neo-Gothic church and the lavish mansion of the Earl de Buisseret. Both were destroyed by the Belgian army at the start of World War I because they obstructed the gunner's view from the local fortifications.

From the 20th century on it was best known for its fortification, built in 1909. It was judged that Antwerp, being continental Europe's second most important port, needed two circles of fortifications for its defence. Breendonk's fortification was part of the outer defensive ring. These fortifications were built on the same site previously occupied by Roman fortifications, this site having been selected because it was the only source of clean water in what until the 18th century was swampland. The modern fortifications fell to the Germans after only a seven day siege.