So on the 7th of May, 1828, the Russians crossed the Pruth and invaded Moldavia and Wallachia,--provinces which had long belonged to Turkey by right of conquest, though governed by Greek hospodars. The Danube was crossed on the 7th of June. The Turks were in no condition to contend in the open field with seventy thousand Russians, and they retreated to their fortresses,--to Ibraila and Silistria on the Danube, to Varna and Shumla in the vicinity of the Balkans. The first few weeks of the war were marked by Russian successes. Ibraila capitulated on the 18th of June, and the military posts on the Dobrudscha fell rapidly one after another. But it was at Shumla that the strongest part of the Turkish army was concentrated, under Omar Brionis, bent on defensive operations; and thither the Czar directed his main attack. Before this stronghold his army wasted away by sickness in the malarial month of September. The Turks were reinforced, and moved to the relief of Varna, also invested by Russian troops. But the season was now too far advanced for military operations, and the Russians, after enormous losses, withdrew to the Danube to resume the offensive the following spring. The winter was spent in bringing up reserves. The Czar finding that he had no aptitude as a general withdrew to his capital, intrusting the direction of the following campaign to Diebitsch, a Prussian general, famous for his successes and his cruelties. In the spring of 1829 the first movement was made to seize Silistria, toward which a great Turkish force was advancing, under Reschid Pasha, the grand vizier. His forces experienced a great defeat; and two weeks after, in the latter part of June, Silistria surrendered. Resistance to the Russians was now difficult. The passes of the Balkans were left undefended, and the invading force easily penetrated them and advanced to Adrianople, which surrendered in a great panic. The Russians could have been defeated had not the Turks lost their senses, for the troops under Diebitsch were reduced to twenty thousand men. But this fact was unknown to the Turks, who magnified the Russian forces to one hundred thousand at least. The result was the treaty of Adrianople, on the 14th of September,--apparently generous to the Turks, but really of great advantage to the Russians. Russia restored to Turkey all her conquests in Europe and Asia, except a few commercial centres on the Black Sea, while the treaty gave to the Czar the protectorate over the Danubian principalities, the exclusion of Turks from fortified posts on the left bank of the Danube, free passage through the Dardanelles to the merchant vessels of all nations at peace with the Sultan, and the free navigation of the Black Sea.