newly-arrived German commander, Frederick Francis II, Grand Duke of Mecklenburg-Schwerin, discontinued his own bombardment. Frederick Francis had been detached to Toul from the Siege of Metz with the 17th Infantry Division, the 17th Cavalry Brigade, three batteries from the 2nd Landwehr Division. The German formations arrived near Toul on 12 and 13 September. The previously engaged German siege forces were redeployed to cover the German supply lines at St. Dizier. German cavalry at Ochey prevented French forces on the Langres plateau from interfering with the siege. The 34th Brigade was deployed on the Choloy plateau, the 33rd on both banks of the Marne–Rhine Canal and the Germans set to work closing in on the glacis from the north. French fire could not stop the German outpost groups, which suffered only 13 casualties. A reconnaissance on 12 September convinced Frederick Francis to begin bombarding the fortress to submission from the south-west. He went off on 13 September to meet King Wilhelm I at Château-Thierry to receive more instructions. On the morning of 15 September, the 2nd Landwehr Division's heavy battery at Mont St. Michel, firing from positions prepared the previous night, harassed for hours the French troops inside Toul and watchposts in the Toul Cathedral tower. The 5th and 6th heavy batteries of the 17th Infantry Division were deployed into pre-prepared positions on Mont St. Michel on 16 September to subdue the French fortress artillery, which had maintained its own fire. Three companies of Prussian heavy artillery with 26 heavy guns and their ammunition arrived by railway from Nancy on 17 and 18 September at St. Robert. Carriages transported the guns to the artillery parks on the Choloy plateau and on the Côte Marine, while their emplacements were being constructed by infantry from Ecrouves. Simultaneously, 42 field guns pounded the fortress on 18 September to distract the French from the transport operation. Colonel Bartsch, commander of the siege artillery, and Major Schumann, the senior engineer officer, planned the direction of the attack. Twelve siege batteries would be used and trenches dug, if necessary. The siege batteries on Mont St. Michel would fire on bastions no. 3 and 4, while fire from La Justice would make a breach on the masonry to the right of bastion no. 4. German pioneers erected a bridge over the river at Pierre la Treiche on 20 September, while a detachment of Bavarian engineers destroyed a canal