After Belgium became independent in 1830, the fear of a European conflict or invasion remained. Because Belgium had no noteworthy natural defense, it was opted not to defend the whole country, but to opt for a 'National Redoubt'. For strategic, political and economic reasons, the city of Antwerp was chosen to become that National Redoubt.

In 1859 the Belgian government decided to defend Antwerp by building a new rampart around the city, called the 'Big Rampart', after a plan of the military engineer Capt. Henri Alexis Brialmont. It consisted of 15 km long earthen rampart with 19 gates around the city.
It also had a ring of 8, almost identical, brick forts. These forts were built almost 2.5 km outside the city, at 2 km from each other. They had to protect the city from enemy fire. Every fort was about 30 hectares and consisted of a central reduit, caponiers, platforms and earthen walls for artillery, all surrounded by a wide moat.

Although building the rampart and forts was a massive and very expensive undertaking, it was finished in 1864. In 1907 the rampart and forts were modernized. The rampart was demolished in 1960. The forts are now more commonly known as the “Brialmont Forts”.

Fort 4 in Mortsel is one of the seven remaining “Brialmont Forts”; it is made from brick with sandstone decorations. Between 1909 and 1911 a gun turret was built in Fort 4, which was later strengthened with concrete. During WW II the German Army occupied this fort and built several barracks. After the war it was used by the Belgian Army up until 2000.