At the Royal Head-quarter in Pont à Mousson it had become known by about noon on the 16th that the IIIrd Corps was engaged in serious conflict, and that the Xth and IXth were hastening up to its support. The far-reaching consequences of this information were recognized at once.
The French were arrested in their withdrawal from Metz, but it was to be presumed as a certainty that they would again make strenuous efforts to force open their interrupted line of retreat. The XIIth Corps was therefore ordered to set out for Mars la Tour as early as three o'clock next morning; the VIIth and VIIIth Corps to stand in readiness at Corny and Arry. The bridging operations were to be pushed with the utmost vigour during the night. The Head-quarter of the IInd Army sent from Gorze the order to the Guard Corps to make a forced march to Mars la Tour, and there take up a position on the left of the XIIth Corps. The execution of these orders was facilitated by the foresight of the Commanders, who had in the course of the day received news of the battle which was being fought. Prince George of Saxony at once placed his Division on the march to Thiaucourt, and the Prince of Würtemberg assembled the Infantry of the Guard in its cantonments farther northward in readiness for an early march.
_August 17th._--On this morning, at sunrise, the French outposts were observed still occupying the sweep of front from Bruville to Rezonville. Behind them were noticed a stir and much noise of signalling, which might be the indications equally of an attack or of a retirement.
The King arrived from Pont à Mousson at Flavigny as early as six o'clock. The reports sent in to headquarters until noon by the reconnoitring cavalry were somewhat contradictory; they left it uncertain whether the French were concentrating towards Metz, or were pursuing their retreat by the two still open roads through Etain and Briey. Preparations for the offensive were nowhere observed. By one o'clock, after a skirmish on the way, the head of the VIIth Corps had reached the northern skirt of the Bois des Ognons, over against which the French subsequently abandoned Gravelotte. The VIIIth Corps stood ready at Gorze, the IXth, IIIrd, and Xth remained in their positions, the XIIth and the Guard Corps were on the march. Seven Corps and three Cavalry Divisions could be counted on for the following day; for to-day all attacks were forbidden.