On October 19, 1916, the situation in Dobrudja again began assuming an unpleasant aspect. On that date Mackensen began a new offensive. Since his retirement a month previous he had remained remarkably quiet, possibly with the purpose of making the Rumanians believe that he had been more seriously beaten than was really the case, so that they might withdraw forces from this front for the Transylvania operations. This, in fact, they had been doing, and when, on the 19th, he suddenly began renewing his operations, the Russo-Rumanian forces were not in a position to hold him back.
After a vigorous artillery preparation, which destroyed the Russo-Rumanian trenches in several places, Mackensen began a series of assaults which presently compelled the Russo-Rumanian forces to retire in the center and on the right wing. On the 21st the Germans reported that they had captured Tuzla and the heights northwest of Toprosari, as well as the heights near Mulciova, and that they had taken prisoner some three thousand Russians. This success now began to threaten the railroad line from Cernavoda to Constanza. This line had been Mackensen's objective from the beginning. On the 23d a dispatch from Bucharest announced that the Rumanian lines had retired again and were barely south of this railroad. Having captured Toprosari and Cobadin, the Bulgarians advanced on Constanza, and on the 22d they succeeded in entering this important seaport, though the Rumanians were able to remove the stores there under the fire of the Russian warships.
[Illustration: General von Mackensen and his staff in Rumania. Already victorious in campaigns in Galicia and Serbia, Mackensen won new laurels in the Dobrudja. His troops pushed on to Bucharest, which fell December 6, 1916.]
On the same date Mackensen began an attack on Medgidia, up the railroad about twenty-five miles from Constanza, and succeeded in taking it. He also took Rasova, in spite of the fierce resistance which the Rumanians made at this point. In these operations Mackensen reported that he had taken seven thousand prisoners and twelve guns. Next he attacked Cernavoda, where the great bridge crossed the Danube, and on the morning of the 25th the defenders were compelled to retire across the structure, afterward blowing it up. Thus the railroad was now in the hands of Mackensen. The Russians and the Rumanians had been driven across the river or up along its bank. But it would be no small matter for the enemy to follow them. With the aid of so effective a barrier as this broad river it now seemed possible that the Rumanians might decrease their forces very considerably on this front, still succeed in holding Mackensen back, and turn their full attention to Falkenhayn in the north. Of course, there still remained the northern section of Dobrudja, passing up east of southern Rumania to the head of the Black Sea and the Russian frontier, along which Mackensen might advance and get in behind the rear of the main Russian lines. But this country in large part constitutes the Danube delta and is swampy, and is certainly not fitted for operations involving heavy artillery. Moreover, Mackensen was now at the narrowest part of Dobrudja, whose shape somewhat resembles an hourglass, and a farther advance would mean an extension of his lines. Aside from this, by advancing farther north, he laid his rear open to a possible raid from across the river, such as the Rumanians had attempted on October 2, 1916, unsuccessfully, to be sure, but sufficiently to show that the whole bank of the river must be guarded. The farther Mackensen advanced northward the more men he would require to guard his rear along the river. For the time being, at least, the river created a deadlock, with the advantage to whichever side should be on the defensive. The Rumanians might very well now have left a minimum force guarding the river bank while they turned their main forces northward to stem the tide of Teuton invasion through the passes.