On 15 January, Blücher issued detailed orders for the operations of the I Corps against the Saar and Moselle fortresses. For the 16th, the field-marshal wanted Prince William's reinforced 8th Brigade to invest Metz on the right bank of the Moselle. Warburg's 2nd Brigade would move east on the Saarlouis–Metz highway to join William at Metz. On the following day, one of the two brigades would cross the Moselle to besiege Metz on the left bank. Blücher also wanted the investment of Thionville and Luxembourg completed on this day. In his cover letter to Yorck, the field marshal authorized the sieges of Metz, Thionville, Luxembourg, and Saarlouis from 17 January onward. “However, in no way is it my intention that this shall be a permanent post,” he explains to his prickly subordinate. Regardless, Blücher emphasized the importance of gaining one of these fortresses as a base of operations for the Silesian Army. Because the majority of the garrisons consisted of conscripts, he believed at least one could be secured through negotiation or taken by storm: “even if we suffer the loss of 1,000 men or more.” He instructed Yorck to have his officers evaluate the strength of each fortress. If any one appeared too strong, the field marshal insisted that Yorck first harass the garrison in order to test its preparedness.