On 16 June, an Austrian-Dutch force of about 43,000 men counterattacked in heavy mist, inflicted 3,000 casualties, and drove Jourdan away from Charleroi back across the Sambre in the battle of Lambusart.

[citation needed] The defeat at Lambusart caused little damage to the French army, with Jourdan sustaining only 3,000 casualties out of a total of 90,000 men under command, of which 70,000 were engaged.

[citation needed] As a result of these factors, Jourdan was quickly ready to go back on the offensive, and he recrossed the Sambre for the fifth time just 2 days after the battle of Lambusart, on 18 June.

[citation needed] Following the previous battle at Lambusart, the Allied high command under Feldmarschall Prince Coburg had assumed that the French were morally and materially beaten, and would be unable or unwilling to undertake another offensive after four successive failures.

[11] Orange ordered his outnumbered force at Chapelle-lez-Herlaimont to withdraw to the main base at Rouveroy to defend Mons and avoid being cut off by French advances.

The 4 battalions intended for Coburg were withheld while Beaulieu's corps, which had returned to guard Namur after Lambusart, was ordered to assemble near Quatre-Bras to cover the road to Brussels.

[citation needed] The third siege of Charleroi commenced formally on 19 June with the city's investment, which the garrison, only 2,800 men strong under one Colonel Reynac,[12] was too weak to delay, especially since no one had expected the French to attack again so soon.

[citation needed] At 7 am on 25 June, seeing that no relief appeared to be forthcoming after a week and that the French were about to begin their third parallel (a trench line close enough to launch infantry assaults from), Reynac asked for terms of surrender.

[16] However, Saint-Just needed to intimidate Reynac into surrendering as soon as possible because the French had been aware for some days that the Allied main army was already nearby and their attack to relieve Charleroi was imminent.

[18] Despite the fact that the French were clearly not ready to assault the fortress yet, Reynac had been discouraged by the apparent lack of any relief, and was intimidated by Saint-Just's posturing and threats.

[citation needed] Coburg planned to bring the 12,000 Austrians under his command at Tournai towards Charleroi to join with Orange's and Beaulieu's 40,000 in the theatre for the decisive battle against Jourdan.

This was exacerbated by a letter which Orange had sent to the high command at Tournai, in which he assessed that Kleber’s attack on his forces at Chapelle-lez-Herlaimont on 20 June was probably intended to cover a retreat, proven by the fact that he was able to reoccupy the town on the 21st with no resistance.

[22] York also offered to bring his corps of British-paid troops to join in the relief of Charleroi, on the basis that this concentration would give Coburg even greater numbers to secure a strong victory that would free him up to then attack the other wing.

[22] After getting York's agreement and arranging for the army's stores to be moved rearward from Tournai to Brussels and Antwerp in case of defeat, Coburg commenced a forced march with his 12,000 men in 13 battalions and 26 squadrons.

[citation needed] During this period, Jourdan also sought to call in Muller's and Scherer's divisions, guarding the right bank of the Sambre further west, to reinforce his army, but he was not given authority over them by the Committee of Public Safety.

[citation needed] While reserves were now available, Jourdan's left wing was now considerably weakened, consisting solely of Montaigu's now-overstretched division, pushed far forward to Trazegnies-Miaucourt (within modern Courcelles), and Daurier's brigade.

Daurier's brigade meanwhile would conduct a fighting withdrawal if needed to defend heights of l’Espinette, within artillery range of the crossings at Marchienne-au-Pont, to prevent the enemy from occupying it and interdicting the army's route of retreat.

Consisting of 7 battalions, 16 squadrons and 16 guns, Peter Vitus von Quosdanovich’s column was to move from Nivelles, where it was located, to Grand-Champ, the plain north of the village of Mellet, on the night of the 25th.

Orange intended to split his column into three: The battle of Fleurus was tactically indecisive, with the French successfully holding the line despite intense fighting, and counterattacking against the Allies in the afternoon despite initial defeats on both their flanks in the morning.

With no siege to relieve, and with the inconclusive fighting and the strength of the French defences and numbers, Coburg decided further attack was not worth the potential gain, and ordered a withdrawal around 3 pm.

They launched relentless combined assaults against the French line throughout the afternoon, but the terrain greatly favoured the defenders, and the Allies made no progress apart from capturing a toehold in Lambusart itself.

[28] The columns began to disengage at around 5 pm, but for Beaulieu, who was attempting to retreat to Gembloux, this coincided with a counterattack on his left flank, launched by Lefebvre, Marceau and reinforcements from Hatry sent by Jourdan.

[29] Meanwhile, Frederic's column had encountered almost no resistance on its advance from Chapelle-lez-Herlaimont, capturing Anderlues and Fontaine l’Eveque and the castle of Wespes[30] before finally being stopped at the heights of l’Espinette by Daurier's brigade, also between 9 and 10 am.

It was at this moment that Poncet's brigade of Montaigu's division, having retreated back across the Sambre at Rus and Marchienne-au-Pont, was ordered to recross and counterattack Frederic at Aulnes to support Daurier's defence.

[31] Opposite the French left centre, Quosdanovich's column marched from Nivelles on the evening of 25 June, passed through Quatre-Bras in the night, and seized Frasne at daybreak on the 26th from a detachment of Morlot's division.

This was provided by a French reconnaissance balloon, l'Entreprenant, operated by a crew under Captain Coutelle of the Aerostatic Corps, which continuously informed Jourdan of Austrian movements.

Representative of the People Guyton, one of the three attached to Jourdan's army, also mentioned in his reports to the Committee of Public Safety that Morlot, whose headquarters was located in Gosselies, spent two hours airborne in the balloon in the morning observing the enemy.

The truth is, this balloon was just plain embarrassing...At the beginning of the action, a general and an engineer entered the gondola to observe, it was said, the enemy movements…but at the height where we let them go up, the details escaped their view and everything was confused.

"[35] Most tellingly, on 3 Pluviose Year VII (22 January 1799), Jourdan recommended in a letter to Barthelemy Scherer, who was Minister of War at the time, that "aerostats (balloons) are not necessary for the army, unless some other way of using them is found."

Smith (1998) wrote: By this stage of the war the court in Vienna was convinced that it was no longer worth the effort to try to hold on to the Austrian Netherlands and it is suspected that Coburg gave up the chance of a victory here so as to be able to pull out eastwards.