When German troops crossed the frontier on 4 August 1914, Belgian planning called for a fighting retreat to Antwerp. The forts at Liege fell first, on 16 August, after Ludendorff personally rallied the assault. Namur fell on 24 August. By 20 August the Belgian government had abandoned Brussels and moved into Antwerp, behind the National Redoubt's twin ring of older inner forts and newer outer forts built after 1882. Three times - in late August, early September and again in late September - the Belgian field army made sorties out of the fortress to cut German supply lines and pull troops back from the drive on Paris. The sorties worked, briefly. They also told the Germans exactly what kind of resistance the Antwerp garrison was capable of.

The forts were built to resist nineteenth-century artillery. They were not built to resist what the Germans brought up after Maubeuge fell: 305mm Skoda mortars and the giant 420mm Krupp howitzers Belgian soldiers nicknamed the 'Big Berthas'. Belgian engineers had cleared the foreground in front of the outer forts so the gunners could see their targets - which also meant German observation balloons could see the forts. Trenches dug between the forts were shallow because the water table was high. There was no overhead cover. When the bombardment opened on 28 September the magazines went first, then the gun emplacements. Fort Sint-Katelijne-Waver was finished by 29 September. Fort Walem fell on 2 October. Fort Koningshooikt fell with it. The Belgian 4th Division had been reduced to a shadow.

On 3 October the British Royal Naval Division began landing at Antwerp, ordered in by First Lord of the Admiralty Winston Churchill in a personal gesture of solidarity that would later be picked over by historians. The Royal Marine Brigade arrived opposite Lier in requisitioned London double-decker buses on 4 October and dug in around the northern fringe of the town - a shallow trench between hedgerows, with one strand of barbed wire in front. They had no artillery to answer the German guns except a single armoured train. On the morning of 5 October two battalions of German Reserve Infantry Regiment 26 crossed the Nete river at Anderstad farm in the fog, under cover of vegetation. By the night of 6 October the German line was within range of the inner forts. King Albert I and his Government posted proclamations warning the inhabitants that they would leave the city.

What the bombardment did to the forts, the bombardment of the city did to the people. The Antwerp waterworks were hit and fires could not be put out. German howitzers began shelling civilian neighbourhoods on the night of 7 October. Roughly a million people - most of the population of the province - left their homes and walked, drove, took whatever boat or train they could find. They went north to the Netherlands, where many were interned at Zeist, Amersfoort, Gaasterland and Oldebroek; west to the coast and Britain; south into France. Most came back eventually. A substantial number never did. The Belgian Military Field of Honour at Harderwijk in the Netherlands still holds the graves of soldiers who died in Dutch internment, far from the country they had been defending. These were ordinary families - shopkeepers, dockworkers, schoolteachers, children - and they lost, in two weeks, the only place they had ever lived.

On 9 October German patrols found the inner forts empty. The Belgian field army had crossed the Scheldt the night before and was already moving west towards Ghent and the coast, leaving a fortress garrison and the British naval brigades to hold the city as long as they could. The Mayor of Antwerp, Jan De Vos, travelled out to the German commander Beseler at Kontich with three other civilian representatives, to beg him to stop the bombardment of the city. Under the threat of its resumption they signed a capitulation on 10 October. The British 1st Naval Brigade, who had not received the withdrawal orders in time, found the Scheldt bridges being demolished as they arrived; about half the brigade was interned in the Netherlands, the other half captured. The Belgian field army made it westward to the Yser river, where it dug in and held the last unoccupied strip of Belgium until the war's end in November 1918.

The Belgian resistance at Antwerp had its strategic effect. The British official history, written by James Edmonds, judged that the prolonged siege detained German troops who were needed at the First Battle of Ypres, and gave the Allies time to occupy the Channel coast. Ostend and Zeebrugge fell unopposed, but Nieuwpoort and Dunkirk were held, which thwarted the last German attempt to turn the Allied northern flank. The siege was a defeat that bought the Allies the foothold from which they would fight the western half of Belgium for the next four years. Antwerp itself remained under German occupation until November 1918. Across the city today, plaques and small monuments still mark fragments of the old fortress ring - the redoubts at Walem, Lier, Kessel - the broken concrete and shattered cupolas left where the super-heavy shells found them.