Since I already have the notes and its fresh in my mind I'm writing up the events of Charleroi and Gilly with the French Right Wing under Grouchy.
Original Post: http://malefricmusings.blogspot.com/2012/01/which-way-to-fleurus-are-we-there-yet.html
The dispositions of Ziethen's I Corps are already covered in the other post. Of interest here is only the that battalions I and III of the 6th Line held the Charleroi. The French had concentrated around Bourmont and Walcourt. Vandamme's III Corps was to support Pajol's calvary on its early morning advance. The courier fell from his horse and Vandamme never recieved his orders and only started marching at 7am as Lobau's VI Corps was stacking up on the road behind Vandamme's Camp.
On a side note Pratt suggests Vandamme wasn't even supposed to be near Bourmont, but instead be advancing with Gerard from Phillipville, but due to confusion in Soult's orders did not concentrate at Phillipville.
Pajol arrives sometime before 10am in the environs of Charleroi. An unspecified cavalry unit surrounds a company of the (unlucky) III/28th Line (Berg) and force their surrender at Couillet, a small outpost in front of Charleroi. Pajol then advanced his hussars against the bridge at Charleroi but meet with the Prussian skirmishers and was repulsed. Vandamme was no where to be seen. Napoleon upon realizing this hurried the movements of the Guard. Napoleon collected the Young Guard's Sappers and Marines and rushed them forward taking the bridge. Pajol was rushed accross the bridge but was met with grapeshot from 2nd Brigades cannon. The Guard then advanced on Charleroi taking it by 11a.m. The Prussians retreated on Gilly.
By 2pm Pirch II had taken up defensive positions on a ridgeline at Gilly. There is some suggestion a detachment of 3rd brigade was present. Other sources just suggest merely contact with the 3rd brigade garrison at Farciennes (III/7th Line + Silesian Schutzen). Basic map of battle is available here: http://napoleonistyka.atspace.com/Gilly_battle.gif
Between 2pm and 3pm Grouchy approaches Gilly with elements of the Guard. He reconnoiters the positions and believes there to be more than 20,000 men on the ridge and woods. Grouchy requests orders from Napoleon who is currently overseeing Rielle on the Left Wing and and awaits Vandamme's Corps. Vandamme crosses the bridge at Charleroi around 3pm. Napoleon returns at approximately 6pm, estimates there to be not more than 10,000 to 11,000 troops in the area and orders an immediate attack. Pirch II following fresh orders for Ziethen begins a withdrawl upon seeing the overwhelming attack approaching his line. Napoleon seeing this retreat orders his guards de service, under Letort to charge. There is confusion as to the manner of the death of Letort--though happily every agrees he did in fact die. The more interesting account suggests he road up to the square of the III/28th (Berg) and demanded they defect. At which point he was shot and the cavalry broke the square of the III/28th in a frenzy. The III/28 lost about 600 men or 2/3 of the battalion. The other units withdrew in squares to the woods. The III/6th Line was in square approximately 500m from the III/28th and held. The cavalry was determined despite increasing losses and multiple sources suggest the III/6th successfully to cut their way through with bayonet the dwindling cavalry to reach the woods before the French infantry arrived. (A rather remarkable reversal.... rarely do infantry charge cavalry!) The Guards de service are only a few squadrons which perhaps explains some of this event, although there were other French cavalry units in the area.
The French harry the 2nd Brigade back on Fleurus and Lambusart. The 3rd brigade is in prepared positions at Lambusart. Artillery fire is exhanged between between French horse batteries and the defenders around 7pm. Night falls soon after and the French make camp along the road; the Prussians fall back on Fleurus.
Gerard and Chatelet:
Where is Gerard's IV Corps? A late start coupled with the defection of Division commander Bourmont bogged down the advance of IV Corps. Chatelet was undefended except for observation scouts. The lead elements of the Corps arrived around 3pm, but the Corps was so spread out over the road Gerard did not get all his troops across the Sambre until the 16th.
Had Gerard been timely, Gilly would have been indefensible. Gerard would have threatened the rear of the ridgeline at Gilly. A timely and vigorious advance by Gerard would have forced the Ziethen to seriously contest the bridge, likely with 3rd Brigade, or risk the very dangerous chance of having both 1st and 2nd brigades cut off from the rest of the Prussian army. If the brigades were lucky they might have been able to retreat north toward Quatre Bras in the event of Gerard cutting their eastward escape route.