The commander of the expedition was Marnix of Tholouse, brother to Marnix of Saint Aldegonde.  This young nobleman, who had left college to fight for the cause of religious liberty, was possessed of fine talents and accomplishments.  Like his illustrious brother, he was already a sincere convert to the doctrines of the reformed Church.  He had nothing, however, but courage to recommend him as a leader in a military expedition.  He was a mere boy, utterly without experience in the field.  His troops were raw levies, vagabonds and outlaws.

Such as it was, however, his army was soon posted at Ostrawell in a convenient position, and with considerable judgment.  He had the Scheld and its dykes in his rear, on his right and left the dykes and the village.  In front he threw up a breastwork and sunk a trench.  Here then was set up the standard of rebellion, and hither flocked daily many malcontents from the country round.  Within a few days three thousand men were in his camp.  On the other handy Brederode was busy in Holland, and boasted of taking the field ere long with six thousand soldiers at the very least.  Together they would march to the relief of Valenciennes, and dictate peace in Brussels.

It was obvious that this matter could not be allowed to go on.  The Duchess, with some trepidation, accepted the offer made by Philip de Lannoy, Seigneur de Beauvoir, commander of her body-guard in Brussels, to destroy this nest of rebels without delay.  Half the whole number of these soldiers was placed at his disposition, and Egmont supplied De Beauvoir with four hundred of his veteran Walloons.

With a force numbering only eight hundred, but all picked men, the intrepid officer undertook his enterprise, with great despatch and secrecy.  Upon the 12th March, the whole troop was sent off in small parties, to avoid suspicion, and armed only with sword and dagger.  Their helmets, bucklers, arquebusses, corselets, spears, standards and drums, were delivered to their officers, by whom they were conveyed noiselessly to the place of rendezvous.  Before daybreak, upon the following morning, De Beauvoir met his soldiers at the abbey of Saint Bernard, within a league of Antwerp.  Here he gave them their arms, supplied them with refreshments, and made them a brief speech.  He instructed them that they were to advance, with furled banners and without beat of drum, till within sight of the enemy, that the foremost section was to deliver its fire, retreat to the rear and load, to be followed by the next, which was to do the same, and above all, that not an arquebus should be discharged till the faces of the enemy could be distinguished.