Both armies, Prussian and Imperialist, began their march for Silesia on the same day, each eager to anticipate and shut the other out. The former marched by the way of Crackau; the latter marched through Bischofswerder; and _en route_ Daun detached Lacy to Keulenburg, to cover his left flank; but Frederick attacked the young brigadier unexpectedly, and captured 200 of his rear-guard. The heat was so excessive at this time that eighty men dropped dead on the march. Lacy continued to harass the Prussian rear, till at Salzforstien Frederick turned and attacked his Uhlans with four regiments of horse, who in the first charge shot and sabred 400 men. At that time Lacy's whole cavalry were encamped at Rothen Nauslitz; but he brought them up by successive troops--for here again he was taken by surprise--and a desultory and destructive skirmish ensued, after which both parties separated. Frederick now decided it was necessary either to follow Daun, who had already reached Silesia, or to rid himself at once of the resolute Lacy, who hung like a wolf upon his skirts, and encumbered every movement. Thus, on the evening of the 8th of July, after making a feigned movement towards Gorlitz, he suddenly broke into Lacy's camp, and drove him beyond the defiles of Horta, where his Prussians passed the night, while the Austrians occupied the mountain of the White Stag. From this Lacy's small force was driven next day, and had to recross the Elbe at Dresden, from whence he marched to a position at Gros Seidlitz, while lines of circumvallation were drawn round the city. A letter written by Daun to Lacy, containing all his plans of the campaign, was intercepted here, and brought to Frederick, to whom it proved of great service.