The safe arrival of Bulow’s Corps at St Lambert, and the reports from his scouts, made Blucher resolve to hasten the march of the First and Second Corps. Pirch’s men had broken up their bivouacs at 5 A.M., but had had to wait until 12 noon to allow Bulow’s Corps to pass clear of Wavre. Zieten, on the left bank of the Dyle, marched for Ohain at noon. Blucher was uneasy about Grouchy’s strength, and his intentions. He was anxious to take his whole army towards Mont St Jean, but he was afraid of an attack on his rear and flank. He therefore determined to leave Thielemann’s Corps at Wavre to await Grouchy’s approach, and if the French were not in strength, Thielemann was to march to join the main body, leaving a small force in Wavre as a rear-guard. Blucher himself, leaving Gneisenau to arrange matters at Wavre, rode on to St Lambert at 11 A.M. While Pirch’s Corps was passing through Wavre, Ledebur’s detachment retired on the town from Mont St Guibert, and the enemy’s cavalry appeared in sight. This was not a pleasant time for action, as the troops were thickly crowded in the defiles and lanes. Sohr’s Brigade of Cavalry, forming Pirch’s rear-guard, fell back, and the Seventh and Eighth Divisions were halted and faced round. The Eighth Division was posted in the wood of La Huzelle, with the Seventh in support. But the French did not press their advance, and at three o’clock, the Prussians retired across the Dyle. Pirch’s Corps then continued its march on St Lambert, leaving Thielemann in defence of Wavre. As a flank march, Blucher’s movement to St Lambert was both a tactical and a strategical success; although under different circumstances, it would have been a failure. For Grouchy should never have allowed it to be carried out. By efficient reconnoitring, such as was carried out by the Prussian Hussars, Grouchy should have discovered the threatened movement early in the morning of the 18th, and have sent Maurin’s Cavalry Division, followed by Excelmans’ Cavalry and Gérard’s Corps, to Moustier and Ottignies. The cavalry could have reached the bridges there in time to threaten Blucher’s flank, and prevent him, if not from assisting Wellington with a part of his forces, at least from throwing his whole weight into the battle against Napoleon. And even at the end, Grouchy might, had he been too late across the Dyle to prevent Blucher from joining Wellington, have covered Napoleon’s retreat, and saved the Emperor’s army from the disastrous rout which befell it. CHAPTER VI THIELEMANN’S INSTRUCTIONS AND HIS DISPOSITIONS AT WAVRE Thielemann had been ordered by Blucher to defend Wavre at all costs if the French appeared in force, but if there was no fear of a serious attack, to leave a small rear-guard there and follow the other three Corps.