10. Armee
In East Prussia, further Russian incursions were blocked by trench lines extending between the Masurian Lakes; they were held by the German Eighth Army, commanded by General Otto von Below. The Eighth Army was reinforced by some of the newly arrived corps, while the rest of them became the German Tenth Army, commanded by Colonel-General Hermann von Eichhorn, which was formed on the German left. The Tenth Army was to be one wing of a pincers intended to surround their opponents: General Sievers' Russian Tenth Army. A new Russian Twelfth Army under General Pavel Plehve was assembling in Poland roughly to the southwest.