The engagement on the 21st opened sensationally. In the early hours of the morning a strong force of Cossack cavalry moved northwards and managed to envelop the German left flank. Dawn was the signal for a combined movement. The Germans found themselves vigorously attacked in the centre and left. For a time they held their ground, but their position soon became untenable. There was no holding the Russian attack. A regiment of Cossacks, finding the ground unsuitable for cavalry operations, dismounted and hurled themselves forward with all their reckless ferocity. Gradually the Russians pressed forward until they were attacking the enemy on three sides. The result was then inevitable. Von Hindenburg had the choice of flight or of allowing his army to be surrounded. He decided to retreat. Soon retreat degenerated into rout, and vast quantities of stores and ammunition, besides thousands of prisoners fell into the hands of the Russians. The battle of Gumbinnen was the first decisive engagement of the war. Its immediate result was to make Russia master of the whole of Prussia east of the line from Königsberg to Allenstein. There was no position which afforded von Hindenburg any hope of successful resistance even if he were able to collect his routed troops. Insterburg, the main point in the network of German strategic railways, fell into Russian hands on the evening after the battle and ensured for Rennenkampf ample supplies. Tilsit was isolated, and its capture was a matter of convenience. The whole region of the Mauer lakes was at the mercy of the Russians. The moral advantages were as great as the material. Von Hindenburg’s army had been badly beaten, and would never be able to face the Russians again with the same confidence. Moreover, the rout of the Germans and the reputation of the pursuing Cossacks caused a panic throughout the province. From every village and town the inhabitants began to fly in terror, some towards Danzig, others towards Graudenz in the hope of reaching Berlin. Soon Danzig was in a state of chaos. Two hundred and fifty thousand refugees poured in with the most exaggerated stories of the prowess of the Russians. Commerce was at a stand-still; the prices of provisions rose daily. Soon there was rioting in the streets. There was no accommodation for the refugees, most of whom were penniless, and who were almost as numerous as the ordinary inhabitants of the town. It was not until the sternest measures had been taken by the military authorities that the panic subsided and some show of order was restored.