Napoleon then entered his carriage, and drove to Quatre Bras. Mounting his horse, he led the pursuit of the English rear. Indignant that Ney had lost the opportunity to overwhelm at least a portion of Wellington's force, he exclaimed to d'Erlon, "They have ruined France!" But he said nothing to Ney himself. So active and energetic was the Emperor that he actually exposed himself to the artillery fire with which the English gunners sought to retard the pursuit. It was not an easy matter for Grouchy to carry out his instructions; at two o'clock began a steady downpour, which lasted well into the next morning; the roads to Gembloux were lanes, and the rain turned them into sticky mud. Not until that night was Grouchy's command assembled at Gembloux; it was ten o'clock before the leader gained an inkling of where the Prussians were, and then, though uncertain as to their exact movements, he immediately despatched a letter, received by Napoleon at two in the morning. The marshal explained that he would pursue as far as Wavre, so as to cut off Bluecher from Brussels, and to separate him from Wellington. Some hours later, about seven in the morning, when finally convinced that the Prussians were retiring on Wavre, Grouchy set his columns in motion in a straight line toward that place by Sart-a-Walhain, choosing, with very poor judgment, to advance by the right bank of the Dyle, and thus jeopardizing the precious connections he had been repeatedly and urgently instructed to keep open. CHAPTER XVI THE EVE OF WATERLOO[23] [Footnote 23: References for this and the following two chapters: Houssaye: 1815, Waterloo; Ussher: Napoleon's last voyage; Ropes: Waterloo; Bustelli: L'Enigma di Ligny e di Waterloo; York: Napoleon als Feldherr; Gardner: Quatre Bras, Ligny, Waterloo; Gourgaud: La Campagne de 1815; Siborne: History of the War in France and Belgium, 1815; Cotton, A Voice from Waterloo; Loben-Sels: Precis de la campagne 1815 dans les Pays-Bas.] Wellington's Choice of Position -- State of the Two Armies -- The Orders of Napoleon to Grouchy -- Grouchy's Interpretation of Them -- Napoleon Surprised by the Prussian Movements -- His Inactivity -- The Battle-field -- Wellington's Position -- Napoleon's Battle Array -- His Personal Health -- His Plan.