At the close of 1916 the Russian Army again had to offer most effective assistance at the critical moment of Mackensen's and Falkenhayn's invasion of Roumania. General Alexeiev pointed out to the Roumanian High Command the excessive length of the Roumanian frontier line which rendered operations in the border district difficult for the small Roumanian Army. General Alexeiev, as well as the Allied military experts, advised the Roumanians to shorten their front line, by means of a retreat, to a shorter line in the East which could be held by the comparatively small Roumanian Army. But the Roumanians, calculating upon a weakening of the Austrians, preferred to choose a new plan and invaded vast Transylvania. [Illustration: This map shows the four places in which the Russian Army, led by Gen. Brussiloff, broke through the Austro-German front in the summer of 1916.] This too daring move, which at first met but feeble resistance, was, however, soon checked by the enemy. When thereupon the enemy himself took the offensive and invaded Roumania and began to threaten Bucharest, the Roumanian representative at Russian headquarters, General Coanda, appealed to Russia for aid. The Russian Army had not yet succeeded in recuperating from the effects of its great summer offensive of 1916. Russia's reserves and supplies had been to a considerable extent spent during the period of Brusilov's offensive. Nevertheless Russia, again as always, did not hesitate for one minute to come to the assistance of the Allies. The Russians even proposed to take upon themselves the defense of the Roumanian capital--Bucharest--but this offer was turned down by the Roumanians with some show of embarrassment; they pointed out that the railroads leading to Bucharest were blocked with evacuated freights from the capital and could not therefore carry the Russian troops. Probably certain political considerations played not a small part in this. However that might be, Russia did not refuse her aid in the form desired by the Roumanians. From the long Russian front which, in turn, stood in need of reserves, troops were taken off and sent to Roumania. Two armies, under Letchitzki and Sakharov, and the great mass of cavalry under Mannerheim, were assigned by the Russians to assist the retreating Roumanians. This effective help by Russia achieved its purpose, stopping the offensive of the enemy, and towards 1917 the Russian Armies also took upon themselves the none too easy task of defending the greater part of the Roumanian front.