A Popular History of The Great War/Volume 1/Page 175
vanguard on the Prussian side of the border, and the reports brought in by the airmen, warned the Germans that the enemy's advanceinforcewasimminent. OnthefollowingdayRennen- kampf crossed the frontier on a broad front right and left of the Gumbinnen railway line, while his southern column, under General Samsonoff, another distinguished leader of the Man- churian War, crossed the border farther south, and began to advance by way of Lyck through the lake region. In the follow- ing days both columns met with a desultory resistance from German detachments, which fell back slowly before them through the woods. The Russian movements in this stage of ihe campaign were constantly watched by ^German aeroplanes* The Russians possessed far fewer of these modem appliances for reconnaissance, and their flying machines, mostly heavy biplanes, were inferior to the German ones, which were Chiefly Taubes, and the flying men, conscious of their lack of speed, were much less enterprising. The German plan of campaign was to delay the advance of the enemy's left column through the lake and forest region by the operations of Landwehr and Landsturm detachments, and to• fight a decisive battle against the right column on the northern line. The place chosen for this stand was at Gumbinnen. Here the railway line, running east and west, and the old high road beside it, crossed the marshy hollow of a little river in the midstofatractofdenselywoodedcountry. Thewesternbank of the river was heavdly entrenched, and thousands of trees were cut down to form long lines of abattis—that is, obstacles con- structed by laying the trees with their branches to the front, and entangling them with barbed wire. Probably over 200,000 men were concentrated for the defence of this hurriedly fortified line. When the work was begun it was not expected that any serious attack could be made on the position by the Russians before the beginning of September. On Sunday, August 16, Rennenkampf had cleared the country up to the Gumbinnen position, and found his further progress arrested by the entrenched line held by the Gemians. According to Russian reports, the enemy's force was made up of three army corps. Allowing for the probability that some oi the reserve formations and local defence detachments had joined them, they would he at least 150,000—and might be perhaps 200,000—strong.