As the Belgian army was ill-prepared and outnumbered by the better-armed and more numerous German troops, the Belgian army had to relinquish control of the strongholds of Liege (which fell on August 16) and Namur, which fell into the hands of the Germans on August 24.
Unable to withstand the massive German offensive, King Albert I of Belgium instructed the army to withdraw to the "Fort of Antwerp" on August 20. This collection of fortifications and defensive positions around the city of Antwerp was considered to be the "reduit national" and impenetrable. The "Fort of Antwerp" consisted of an outer and an inner ring around the city of 19th-century forts and strongholds within a distance of several kilometers of each other, built to defend the vital harbor of Antwerp. Remnants of these fortifications can still be seen today and most are now recreational areas.
Most Antwerp forts and defensive positions were hopelessly outdated and lacking in firepower. The German army, better armed and technologically more advanced, attacked the city of Antwerp on September 28, preceded by a heavy artillery barrage. Antwerp was besieged and the forts of the outer ring fell one by one between October 1 and October 4. The Belgian soldiers suffered from fatigue and were demoralized due to heavy terrain losses.
October 5 was a crucial date during the Siege of Antwerp; the German army broke through the Belgian defences in the town of Lier, 20 kilometers southeast of Antwerp and moved on to the town of Dendermonde (south of Antwerp) where it attempted to cross the river Scheldt. This "pincer movement" of the German army threatened to block the western retreat route of the Belgian army out of Antwerp, its eastern and southern escape routes being blocked by German troops and its north blocked by the closed Belgian-Dutch border. The Dutch did not offer any assistance, not wanting to be drawn into the conflict, preferring neutrality.
The Belgian army retreated before being trapped and left the city of Antwerp to its own defenses. Belgian forces fled westwards towards the coast on October 6 eventually stopping the German advance on the banks of the river Yser. The city of Antwerp was defended by the remaining fort's garrisons. Most of these troops were abandoned by their officers and many soldiers deserted and destroyed their own weaponry and ammunitions.
One third of the Belgian Army, about 40,000 soldiers, fled north to the Netherlands, followed by one million civilian refugees in 1914. The Netherlands interned Belgian refugees as far as possible from the Belgian border, for fear of being drawn into the conflict, many continued living in the Netherlands after 1918 and never returned to Belgium.