The French invaded from the south and defeated the Spanish army at Les Avins on 20 May, eventually joining forces in Maastricht with Frederick Henry of Orange, who had departed the Dutch Republic in command of 20,000 infantry and 6,000 cavalry soldiers,.

[9] Meanwhile, the Cardinal-Infante Ferdinand, who was in Leuven, ordered the Spanish Tercios to move to Tienen and sent the Count of Fuenclara to Germany with instructions to call the Imperial army for help.

[9] The joint army of France and the United Provinces, then numbering 50,000 men,[9] composed by French, Dutch, German and English soldiers,[9] marched to Tienen, defended by a small garrison under Captain Martín de los Alarcos.

Nevertheless, they remained inactive for eight days, which allowed the populace of all the country, but specially of Brussels, where the news of the sack of Tienen had caused great fear, to escape to safer places.

[5] The Spanish troops spent two hours observing the Franco-Dutch forces moving over the hills of the opposite riverside, when they discovered that they were crossing the Dijle using an undefended footbridge located a league from the first one.

[5] Seeing this, the Duke of Lerma ordered Celada to withdraw, warning him through Captain Diego de Luna that he could not relieve him if his men were attacked, as the cavalry under Johann von Nassau-Siegen had fallen behind.

[5] That night all the artillery and baggage marched back to Brussels, and the following day so did the Cardinal-Infante with his camp,[10] leaving the defense of Leuven in charge of the veteran Anthonie Schetz, baron of Grobbendonck.

[11] Much of the failure was caused by the fact that the maneuvers of his army were being observed from a well-fortified tower, situated between the gates of Mechelen and Vilvoorde, popularly called Verlooren-Kost.

[1] A party of 500 German mercenaries under Lt.-Col. Eyndhouts, roaming on his left flank, managed to surprise the Dutch fortress of Schenkenschans that at the time had a garrison of only 120 soldiers, in the night of 27/28 July.

Frederick Henry personally started the siege of Schenkenschans within days of its fall, but soon transferred command to his cousin John Maurice, Prince of Nassau-Siegen.