Meanwhile the Russian diplomatists discovered that the Emperor of Austria, Charles VI, was quite as anxious as the Czarina Anne to possess himself of Turkish provinces, and was ready to enter into a coalition for the purpose. In the winter of 1736-7 a secret treaty for this purpose was entered into between the two potentates. But as it was not thought expedient by the Austrians to commence their attack until all their preparations for it were completed, a pretence was made of negotiations with the Porte, who had made overtures of peace to the Russians. For this purpose a Congress was held at Nimirof early in 1737. Later it became known that the negotiations on the part of the two allied Empires were illusory, and that there never was any intention to come to terms. The Porte, on its part, was extremely anxious for peace, and was ready to make large concessions, but the terms suggested on behalf of Russia were so extortionate that it was quite impossible for the Sultan and his ministers to entertain them. The Russians demanded the cession of the Crimea, the independence of Wallachia and Moldavia under a native prince, subject to the supremacy of Russia, the opening of the Black Sea and access to it through the Bosphorus and the Dardanelles to Russian vessels of war, and the payment of fourteen millions of roubles. Austria, on its part, demanded the cession of the whole of Bosnia and Serbia. Such terms could only be assented to by the Porte after complete and disastrous defeat. They were indignantly rejected, and, much against the wish of the Porte, the Congress came to an end, and the Sultan was forced to take up arms in defence of his Empire. A Russian army of seventy thousand men, under Marshal Munnich, opened the campaign of 1737 by an attack on Oczakoff, the most important of the Ottoman fortresses on the northern shores of the Black Sea, and General Lascy, with forty thousand men, again invaded the Crimea. Oczakoff was vigorously defended by twenty thousand Turks. After some days of siege the principal powder magazine in the fortress blew up, causing enormous destruction and loss of life. The Turkish general, dismayed by this, capitulated on favourable terms. But this did not prevent the massacre of the greater part of the garrison, and only three thousand of them survived. The losses of the Russians, chiefly by disease, were also very great, and nothing more was done by Munnich in this year’s campaign. Meanwhile Lascy in the Crimea had repeated the operation of Munnich of the previous year, and eventually retreated from it. The Austrians, on their part, invaded Bosnia and Serbia with two armies. The principal one, under General Seckendorf, attacked and captured Nisch and, later, Widdin. But this exhausted their efforts for the year, and most of their army perished from disease in the marshes of the Danube.