It was between three and four o'clock when the Advanced Guard of the Third Brigade, consisting of the 1st Silesian Hussars, two Rifle Companies, and a Fusilier Battalion, arrived in front of the Fortress of Avesnes. The Commandant having rejected Zieten's summons to surrender, the latter ordered the bombardment to be commenced forthwith. Ten Howitzers, of which six were ten pounders and four seven pounders, drew up on the Flank of the Cavalry, and fired upon the Town. The houses of the latter being all strongly built, the shells failed in setting any part on fire; and a twelve pounder Battery produced no great effect upon the firm masonry of the works. At nightfall the bombardment was suspended; with the intention, however, of resuming it at midnight. When it ceased, a sortie was made by the French Tirailleurs; but these were immediately encountered and gallantly driven in by the Silesian Rifles, who lost ten men on this occasion.
Immediately after midnight, the Prussian Batteries recommenced their fire. At the fourteenth round, a ten pounder shell struck the principal Powder Magazine, when a tremendous explosion ensued, by which forty houses were involved in one common ruin; but it occasioned no damage whatever to the fortifications. The panic, however, which it created amidst the garrison was such as to induce the latter to express its desire to capitulate. Such a desire could only have proceeded from the want of sufficient energy on the part of the Commandant, or from a bad disposition evinced by the garrison; for when the Prussians subsequently entered the place, they found in it 15,000 cartridges for cannon, and a million musket ball cartridges. There were also in the Fortress forty seven pieces of artillery, mostly of heavy calibre; which were now made available in the besieging of the remaining Fortresses. The garrison, comprising three Battalions of National Guards, and two hundred Veterans, were made prisoners of war. The National Guards were disarmed, and sent off to their respective homes; but the Veterans were conducted to Cologne.
The possession of Avesnes, gained too with so little sacrifice of life, and with none of time, was of essential importance to the Prussians; offering as it did a secure depôt for their material and supplies upon their new line of operation. It also served for the reception of their sick, and all who had been rendered incapable of keeping up with the Army.
On the 21st, the French Army continued collecting its scattered remnants between Avesnes and Laon.
The following was the general disposition of the respective Armies on the evening of the 21st:
The Anglo-Allied Army had its principal force at Bavay; and its Right at Valenciennes, which it blockaded.
The Duke of Wellington's Head Quarters were at Malplaquet.
The Prussian Army had its First Corps d'Armée near Avesnes.
The Fourth Corps at Maroilles; its Reserve Cavalry blockading Landrecy.
The Second Corps at Thuin, except the Fifth Brigade which blockaded Maubeuge.
The Third Corps at Charleroi.
Prince Blücher's Head Quarters were at Noyelles sur Sambre.
The defeated portion of the French Army lay between Avesnes and Laon.
Grouchy's force was at Philippeville.
The Duke of Wellington, steadfastly pursuing that line of policy which led him to constitute as an important feature of his plan, the practical assurance to the French people, that, although entering their country as a Conqueror, he did so in hostility to none, save the Usurper and his adherents, issued the following Proclamation, previously to his quitting Malplaquet:—