The Battle of the Niemen River (sometimes referred to as the Second Battle of Grodno) was the second-greatest battle of the Polish–Soviet War. It took place near the middle Neman River between the cities of Suwałki, Grodno and Białystok. After suffering almost complete defeat in the Battle of Warsaw (August 1920), Mikhail Tukhachevsky's Red Army forces tried to establish a defensive line, against Józef Piłsudski's counter-attacking Polish Army, running northward from the Polish-Lithuanian border to Polesie, and centering on Grodno. Between September 15 and September 25, 1920, the Poles outflanked the Soviets, once again defeating them. After the mid-October Battle of the Szczara River, the Polish Army had reached the Tarnopol-Dubno-Minsk-Drissa line. Although this part of the conflict is usually referred to as a battle both in Polish and Russian historiography, some historians argue that it was more of a military operation with a series of battles fought often several hundred kilometres apart. Prelude Following the Battle of Warsaw in mid-August, the armies in the centre of the Russian front fell into chaos. Mikhail Tukhachevsky ordered a general retreat toward the Bug River, but by then he had lost contact with most of his forces near Warsaw, and all the Bolshevik plans had been thrown into disarray by communication failures. Russian armies retreated in a disorganised fashion, with entire divisions panicking and disintegrating. The Red Army's defeat was so great and unexpected that, at the instigation of Piłsudski's detractors, the Battle of Warsaw is often referred to in Poland as the "Miracle at the Vistula". Previously unknown documents from Polish Central Military Archive found in 2004 proved that the successful breaking of Red Army radio communications ciphers by Polish cryptographers played a great role in the victory. Although successful, the Polish counter-attack in the battle of Warsaw created an awkward situation for Polish commander in chief Józef Piłsudski. Most of his forces were facing north while Russian heartland was located east of the front rather than north. Because of that, the Polish Army needed some time to reorganise and regroup before a new offensive could be mounted. The Russian commanding officer Mikhail Tukhachevsky took this as an opportunity to establish a new defensive line along the Niemen River, initially safe from Polish forces. The new Soviet line ran from the Russian-Lithuanian demarcation line in the north, to the dense forests and swamps of Polesie, with the city of Grodno (modern