... attack upon Tilly, the Elector might again open his fortresses to the Imperialists, and the king, with an enemy both in front and rear, would be irrecoverably lost. In order to prevent this contingency, he demanded that the Elector should allow him to hold the fortresses of Custrin and Spandau, till the siege of Magdeburg ... — The Works of Frederich Schiller in English • Frederich Schiller
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