The summer of 1759 again found the Russian troops spread over the Prussian territory. In great force the two hostile armies soon met on the banks of the Oder. The Russians, posted upon a line of commanding heights, numbered seventy thousand. Frederic fiercely assailed them through the most formidable disadvantages, with but thirty thousand men. The slaughter of the Prussians was fearful, and Frederic, after losing nearly eight thousand of his best troops in killed and wounded and prisoners, sullenly retired. The Russian troops were now strengthened by a reinforcement of twelve thousand of the choicest of the Austrian cavalry, and still presenting, notwithstanding their losses, a solid front of ninety thousand men. Frederic, bringing every nerve into action, succeeded in collecting and bringing again into the field fifty thousand troops.[16] Notwithstanding the disparity in numbers, it seemed absolutely necessary that the King of Prussia should fight, for the richest part of his dominions was in the hands of the allied Prussians and Austrians, and Berlin was menaced. The field of battle was on the banks of the Oder, near Frankfort. [Footnote 16: Some authorities give the Russians eighty thousand and the Prussians forty thousand.] On the 12th of June, 1759, at two o'clock in the morning, the King of Prussia formed his troops in battle array, behind a forest which concealed his movements from the enemy. The battle was commenced with a fierce cannonade; and in the midst of the thunderings and carnage of this tempest of war, solid columns emerged from the ranks of the Prussians and pierced the Russian lines. The attack was too impetuous to be resisted. From post to post the Prussians advanced, driving the foe before them, and covering the ground with the slain. For six hours of almost unparalleled slaughter the victory was with the Prussians. Seventy-two pieces of cannon fell into the hands of the victors, and at every point the Russians were retreating. Frederic, in his exultation, scribbled a note to the empress, upon the field of battle, with the pommel of his saddle for a tablet, and dispatched it to her by a courier. It was as follows: "Madam: we have beat the Russians from their entrenchments. In two hours expect to hear of a glorious victory."