Novo-Georgievsk was a great Russian fortress north west of Warsaw. It was defended by a series of outer forts, the most modern of which had been built in 1891. Its defences had been modified during the first year of the First World War.
At the start of August 1915 the Russians were on the verge of abandoning Warsaw. The Germans had broken through their lines at Gorlice-Tarnow (2-10 May), and had forced the Russians back all along their southern front. During July the Germans had then turned north, and were advancing to the east of Warsaw. On 13 July a second German army attacked towards the Narev river, north of Warsaw. By the end of July the first German troops were approaching Novo-Georgievsk.
At this point, with Warsaw about to be abandoned, the Russians should have evacuated Novo-Georgievsk. Instead, the Grand Duke Nicholas decided to defend the fortress and left its garrison of 90,000 in place. If this had been done in an attempt to delay the German advance on Warsaw it failed, for the city was evacuated on 5 August, ten days before the siege of Novo-Georgievsk began.
The Germans diverted 80,000 men to the siege, mostly from second-line formations. They were given part of the siege train used at Antwerp in 1914, including six 16 inch (400mm) and nine 12 inch (300mm) howitzers, and were placed under the command of General von Beseler, the German commander who had captured that city.
Novo-Georgievsk was completely surrounded on 10 August. The bombardment began a few days later, and concentrated on the north eastern segment of the defences, north of the Vistula. After a heavy bombardment three of the outer forts were attacked by twenty four German battalions and two of them captured. By the end on 19 August the Russians had been forced back to the inner defences north of the Vistula.
With no hope of being relieved and with their inner defences now vulnerable to bombardment, at 4 a.m. on 20 August the Russian defenders of Novo-Georgievsk surrendered. The Germans took 90,000 prisoners, amongst them thirty generals, and captured 700 guns. The siege of Novo-Georgievsk was the last time during the First World War that any side attempted to defend an isolated fortress of this type, ending a sequence that had included the sieges of Liege, Namur, Antwerp and Przemysl, each of which had eventually ended in the surrender of the fortress.