The Left Wing of the Prussian Army, comprising the Third, and part of the Second, Corps d'Armée, came into collision with the Enemy this day, when pursuing that part of the French Army which was under Grouchy. Thielemann, having learned that the latter had commenced his retreat upon Gembloux, marched at five o'clock in the morning from St Achtenrode to Wavre; where he further ascertained that already on the afternoon of the 19th, the French had effected their retreat across the Dyle, leaving only a Rear Guard on the left bank of the river.
Grouchy, when he decided on retiring upon Namur, ordered General Bonnemains to move on rapidly, by Gembloux, with the 4th and 12th Dragoons, as an Advanced Guard, and to reach that town as soon as possible, and secure the passage of the Sambre. They were followed by the remainder of Excelmans' Cavalry, and the Reserve Artillery, together with the wounded. The Infantry was put in motion in two Columns: the one, consisting of the Third Corps d'Armée, proceeding by Gembloux; and the other, comprising the Fourth Corps, passing more to the right, and falling into the Namur road in rear of Sombref. The Light Cavalry was principally with the Rear Guard. To deceive Thielemann, Grouchy left his Rear Guard in Wavre and Limale, with Cavalry Picquets thrown out towards the Prussians, until near evening; when it followed the main body to Namur.
Thielemann, having placed the whole of his Cavalry, with eight pieces of Horse Artillery, at the head of his Column, now ordered them to move on at a trot, for the purpose of overtaking the Enemy; but it was not until they had passed Gembloux that they discovered the Rear of Grouchy's force, consisting of a few Regiments of Cavalry. These, however, now made so rapid a retreat, that it was impossible to bring them to action.
At length, on arriving near the Village of Fallize, within about three miles from Namur, the Prussians found Vandamme's Rear Guard posted on the brow of the declivity at the foot of which lay the town, in the valley of the Meuse. It presented about two Battalions of Infantry, three Regiments of Cavalry, and four guns; and was formed to cover the retreat of the French troops.
The Prussian Battery immediately opened a fire; during which Colonel Marwitz, moving out to the right, with the First Cavalry Brigade, and Count Lottum to the left, with the Second, turned the Enemy in both Flanks. The latter brought forward a Reserve of Cavalry, when the 8th Prussian Uhlans, under Colonel Count Dohna, at the head of the Column that turned the Enemy's Left, made a most gallant attack upon the French Dragoons; who met it with a volley from their carbines, but were overthrown. The 7th Uhlans and a Squadron of the 12th Hussars also charged on this occasion, and captured three pieces of French Horse Artillery, which were in the act of moving off, as also fifty Cavalry horses. The Enemy's Infantry now threw itself into the adjacent Wood, with which the declivities that here lead down into the valley of the Meuse are covered, and thus succeeded in preventing the Prussians from following up their success.
At this moment, intelligence was received that General Pirch was pursuing the Enemy with the Second Corps d'Armée upon the high road leading from Sombref to Namur; whereupon the Cavalry of the Third Corps was moved into this direction. A French Column, consisting of about twelve Battalions and two Batteries, but without any Cavalry, was perceived marching along that road. They belonged to Gérard's Corps d'Armée, which had effected its retreat by Limale, through Mont St Guibert. Upon the Height on which the Château of Flavinnes is situated was posted a Detachment from Vandamme's Corps, consisting of from four to five Battalions with a Battery, and a Regiment of Cavalry, for the purpose of receiving Gérard's Column as it fell back, and of protecting its retreat. As the Enemy continued its retrograde march in Close Column and in good order; it was not deemed advisable to undertake an attack with the two Prussian Cavalry Brigades of the Third Corps, which were much fatigued: but the Horse Battery was drawn up, and discharged several rounds of shell and grape at the French troops during their retreat upon the town. The latter, therefore, quitted the high road, and moved along the adjacent Heights until they reached the Battalions which had been drawn up in support, and which now opposed the further advance of Pirch's Corps d'Armée.
At this time, Thielemann's Cavalry withdrew, leaving the further pursuit of the Enemy to the latter Corps—to the movements of which it is now necessary to recur.
It was not until five o'clock in the morning of the 20th that Pirch received intelligence that the Enemy was retiring by Gembloux upon Namur. Lieutenant Colonel Sohr was immediately detached, in all haste, to Gembloux with his Cavalry Brigade, a Battery of Horse Artillery, and the Fusilier Battalions of the 9th, 14th, and 23rd Regiments, as an Advanced Guard. On approaching that town, Lieutenant Colonel Sohr ascertained that Thielemann's Cavalry was pursuing the Enemy along the high road from Gembloux to Namur. He therefore decided upon marching by the narrow road on the right of the chaussée leading from Sombref, in full trot, covered by the Wood, to overtake the French troops in retreat. At Temploux, the latter presented a force of two Battalions, some Cavalry, and four pieces of Artillery in position, prepared to cover the retreating Column. Lieutenant Colonel Sohr immediately attacked with both the Regiments of Hussars, supported by the Battery of Horse Artillery; and defeated this portion of the Enemy's forces. It was at this moment, too, that a cannonade was opened upon the latter by the Horse Battery, before mentioned, of Thielemann's Corps; whereupon it fell back upon the favourable position taken up near Flavinnes, and in which the Enemy appeared determined to make a stand.