[2] Following the dominance of the Spanish forces, led by Duke Emmanuel Philibert of Savoy, at the Battle of St. Quentin, Henry II of France prepared his revenge.

Francis, Duke of Guise, seized the port of Calais from the English and moved to capture the city of Thionville in Philip II's duchy of Luxembourg on 22 June 1558.

After crossing the river Aa at its mouth, de Thermes commandeered his army to conquer both Dunkirk and Nieuwpoort, consequently threatening Brussels.

Surprised by the speed of the Spanish maneuver, Thermes had to do battle because he had the river behind him, the sea on his left, and his right completely blocked by the baggage column of his own army.

Biscay and English ships under Admiral Edward Clinton bombarded the French rear, causing numerous casualties.