VANDAMMME did not reach Charleroi until three o'clock in the afternoon, when he received Orders to pursue the Prussians, in conjunction with GROUCHY, along the Fleurus road. It was, however, a considerable time before any advance was made. In the first place, the whole of VANDAMME's Corps had to cross the Sambre by a single Bridge; secondly, both Generals were deceived by exaggerated reports concerning the strength of the Prussians in rear of the Fleurus Woods; and GROUCHY who had gone forward to reconnoitre, returned to the Emperor with a request for further instructions. Upon this, NAPOLEON undertook a reconnaissance in person, accompanied by the four Squadrons _de Service_; and having formed an opinion that the amount of force in question did not exceed 18, or 20,000 men, he gave his Orders for the attack of General PIRCH's Brigade. The French Generals having directed their preparatory dispositions from the Windmill near the Farm of Grand Drieu, opened the engagement about six o'clock in the evening, with a fire from two Batteries. Three Columns of Infantry advanced in echelon from the right, the first directing its course towards the little Wood occupied by the Fusilier Battalion of the 6th Prussian Regiment; the second passing to the right of Gilly; and the third winding round the left of this Village. The attack was supported by two Brigades of General EXCELMANS' Cavalry Corps, namely, those of Generals BOURTHE and BONNEMAIN; of which one was directed towards Châtelet, thus menacing the Prussian Left Flank, and the other advanced along the Fleurus road. The Battery attached to the Second Prussian Brigade was in the act of replying with great spirit to the superior fire from the French Artillery, and the Light Troops were already engaged, when General PIRCH received ZIETEN's Orders to avoid an action against superior numbers, and to retire by Lambusart upon Fleurus.