From Losnitza, where the main column of Austrians crossed the Drina to Valievo, runs the River Jadar, along a level valley, which narrows as it nears Valievo. On the left-hand side of the Jadar Valley rise the southern slopes of the Tzer Mountains, covered with cornfields, prune orchards, with here and there a stretch of thick timber. Continuing southward, slightly to the eastward, up the Jadar Valley another range rises, slightly smaller than the Tzer Mountains, forming a smaller valley which branches off eastward. Along this runs the River Leshnitza, parallel with the Jadar until it makes an independent junction with the Drina. Still farther up the valley the foothills of the Iverak ridges are lost in a series of fairly important summits which closely flank the Jadar River. To the south of the Jadar River the valley stretches into a rolling plain, which rises abruptly into the giant Guchevo Mountains. It is this range, converging with the Tzer and Iverak Mountains toward Valievo, and forming the plain of the Jadar Valley, which was presently to become the center of the first great battle between the Serbians and Austrians. A military movement against Valievo, therefore, demanded complete possession of these two ridges, which overlooked the line of march. This the Austrians knew well enough, even before the first of their troops had crossed the Drina. As is well known, the best maps, not only of Serbia but of all the Balkan countries, have been made by Austrian engineers. There was probably not a spur, not a fissure, certainly not a trail, of these mountains that had not been carefully surveyed and measured by engineers of the Austrian staff. The Austrians knew the country they were invading quite as well as did the native Serbians. All through it may be said that it was not through want of accurate knowledge that the Austrians finally met disaster. Rather was it because they misjudged the relative values of their facts. And one of their first mistakes was in overestimating the effects of the two Balkan Wars on the efficiency of the Serbian army. First of all, as was obvious from the leisureliness with which they proceeded to occupy the two mountain chains in question, that they vastly misjudged the capacity of the Serbian troops to make rapid movements. Even as the first shots were being fired across the Drina at Losnitza, the Serbian forces were on the move, westward. Two army corps were at once rushed toward the Valley of the Jadar; part of a third was sent to block the advance of the Austrians from Shabatz. Meanwhile the Austrians took their time. For two days they busied themselves fortifying the bridge at Losnitza. CHAPTER XLIX THE GREAT BATTLES BEGIN