On July 13, 1622 the contract was cancelled and the unemployed army of Mansfeld and Christian of Brunswick was hired by the Dutch to help in the relief of the siege of Bergen-op-Zoom.

The Protestant army departed from Alsace and at a fast pace[1] crossed Northern France, entering the Spanish Low Countries through Hainaut.

Cordoba marched through the Duchy of Luxembourg and the difficult terrain of the Ardennes, and was able to intercept Mansfeld and Brunswick on the border of Brabant.

Córdoba, much weaker in cavalry, had assumed a blocking position north of the town of Mellet, near Fleurus, with flanks supported by woods.

It included the elite Tercio of Naples, which traced its history back to 1567, and had recently lived up to its reputation with a superb performance at the Battle of Wimpfen.

Some gaps opened up in the poorly drilled German infantry, and De Sylva attacked an exposed flank, routing one Battalion.

After five hours of fighting, Mansfeld ordered a general retreat, it was midday and he intended to take the road through Liège around Córdoba to reach Breda.

[7] As the Spanish army had failed to block Brunswick and Mansfeld, Spinola was compelled to lift the siege of Bergen-op-Zoom, although the outcome of Fleurus bought him space to retreat safely.