Just previous to the fall of Warsaw the eastern front, roughly speaking, was formed by the two sides of an equilateral triangle, with the northern side starting from a point on the Gulf of Riga, about forty miles northwest of Riga, and with the southern side starting from Chotin on the River Dniester in Russian Bessarabia, very close to the point where that Russian province touches Rumania and Galicia. The apex was at Warsaw. When this apex caved in with the withdrawal of the Russians, it followed logically that something had to happen to the two lines that met there. That the Russians retreated from Warsaw on account of some insurmountable difficulties which made the further holding of this most important center impossible, is quite clear. It has been established by now, almost beyond all doubt, that this step became necessary because of insufficient munitions. But whether this is so or not, it still remained true that whatever caused their retreat from Warsaw would exert a similar influence on their capacity to hold their second line of permanent fortifications. And events immediately following the fall of Warsaw proved this contention. Backward and backward fell the Russian lines during the following weeks until by the end of October, 1915, the two sides of the erstwhile triangle had disappeared entirely, and the Russian front was found now along the base of the triangle stretching from Riga through Friedrichstadt, through a point somewhat west of Dvinsk, thence almost due south, skirting Pinsk slightly to the east, and again running south in front of Rovno, entering Galicia at a point about halfway between Zlochoff and Tarnopol, and following, slightly to the west, the River Sereth to a point on the Dniester only a few miles west from where it had ended in August, 1915.