Gustavus well knew that if he left Brandenburg, Berlin would follow Magdeburg, so, as he retreated from Spandau, either as a huge joke or in earnest, he planted his artillery to command the city of Berlin. The ladies of the Elector's family came in person to entreat Gustavus not to move north and leave them to the mercy of the Imperialists, and to beg him not to shell the city. They assured him that the Elector would treat with him, make any treaty—only Gustavus must not leave the Duchy to the fate of Magdeburg. Munro says: "And the king answered, merrily, that if the Duke did not conclude a treaty with him before night he would send the Duchess and all the ladies prisoners to Sweden, and that the Duke should follow." The alliance was concluded June 11th, Gustavus to hold Spandau during the war, and to have free passage through Kustrin and to use any other fortresses he might need. A payment of thirty thousand dollars a month and liberal contributions for the support of the army were also granted. About this time Gustavus learned that Greifswald, the only fortress which the Imperialists yet held in Pomerania, had surrendered to the Swedish General Ake Tott. The Czar of Moscow sent messengers to congratulate him, also to renew his alliance and to offer him troops. Gustavus was much gratified at this attitude of Russia, as it was most desirable to keep Sweden undisturbed by any foreign foe while its king was absent from his country. The latter part of June Gustavus employed in reinstating the Dukes of Mecklenburg, who were now put into full possession of all their duchy, except Rostock and Wismar. They proved very ungrateful, and General Ake Tott had great difficulty in making them furnish their share of contributions for the war which gave back to them their possessions. General Tilly now marched direct from Magdeburg to Thuringia, in order to force the Landgrave of Hesse to disband the troops he had gathered for the assistance of the king of Sweden, also to force him to receive Imperial garrisons in his fortresses, and to pay a large war indemnity. Of course, he refused to comply with these demands. As Tilly passed over the country everything was laid waste. His army had been almost as demoralized by the victory at Magdeburg as if it had been a defeat. The men of the army seem never to have desisted even for a single day from robbery, arson and all forms of nameless crimes. Meanwhile, General Bauer, of Gustavus' army, had stormed Havelberg, so that now the Swedes held nearly all the country north of the Elbe, and were ready to take the aggressive. But think of it, he had been obliged to conquer the duchies of Mecklenburg and Brandenburg, whose princes were Protestants and should have been more interested in bringing the army supplies, furnishing troops and driving back the Imperialists, than Gustavus himself. It was not their religion, but their lack of religion that was at fault.