It is not necessary to enter here into the details of the retreat of Zieten and Pirch I., except in so far as they bear upon the subject of Thielemann’s withdrawal, but a brief description of their movements may be given. The two Corps retreated by the roads Tilly-Mont St Guibert and Gentinnes-Mont St Guibert. Pirch’s Corps, arriving second, remained at Mont St Guibert for a time as rear-guard, to protect the cross-roads, and still further to steady the men; for the best troops are unsteadied by retreat. Zieten pushed on to Wavre, arriving at noon, and took his troops across the Dyle, halting at Bierges, about a mile south-west of the town. Pirch followed, but did not cross the Dyle; he halted between Aisemont and St Anne, two villages a mile and two miles south-east of Wavre. Gneisenau had given Thielemann the choice of retreating upon Tilly or Gembloux, a point which could only be decided according to circumstances. Both of these places were on roads converging upon Wavre, and at Gembloux there were no less than four alternative routes. When Thielemann made preparations for his retreat, he considered carefully the respective advantages of these two points. If he chose Tilly, he would have to make a flank march along the Namur road to Marbais and strike northwards from there. He would then be following the road taken by Pirch I. and Zieten; but this very fact was an objection, because there were sure to be disabled waggons, broken-down guns, and hundreds of stragglers to hinder his passage. He could only use one road, too. But was it safe to expose himself to an attack on his flank by the French, while he was marching on Marbais? Certainly not; for he could not possibly slip by in the darkness; it would be daylight before his rear had cleared Sombreffe. He turned to Gembloux. The road from Sombreffe to that village was direct. He would not expose either flank by marching along that road. It was not encumbered with the remnants of a retreating force; and his troops were already in an easy position to withdraw. At Gembloux, he might expect to meet Bulow’s Corps; and if so, the two could unite and use any of the four roads from thence towards Wavre. It would save a great deal of time if he could employ more than one road for his march, but he would have to make ample provision for guarding the rear of his columns, and it would be more difficult to protect three columns than one. He expected to be closely pursued the moment he began to retreat, but he would leave a strong rear-guard to cover him. But it must be remembered that Thielemann, at this time, did not know whither the retreat was ordered, beyond Gembloux. He guessed that it was in the direction of Wavre on account of the route taken by the First and Second Corps.