It was the actual course of events which transcended experience and set all probabilities at defiance.
The battle of Gravelotte, or St.Privat, on the 18th completed the work so hardily begun by the 3rd German corps on the 16th.

The need of driving back Bazaine's army upon Metz was pressing, and his inaction on the 17th gave time for nearly all the forces of the First and Second German Armies to be brought up to the German positions, some nine miles west of Metz, though one corps was left to the east of that fortress to hinder any attempt of the French to break out on that side.

Bazaine, however, massed his great army on the west along a ridge stretching north and south, and presenting, especially in the southern half, steep slopes to the assailants.

It also sloped away to the rear, thus enabling the defenders (as was the case with Wellington at Waterloo) secretly to reinforce any part of the line.

On the French left wing, too, the slopes curved inward, thus giving the defenders ample advantage against any flanking movements on that side.