Alva could not be induced to withdraw any portion of the army that was closely blockading Mons, but contented himself in following Orange with a force under his own command while avoiding a general action.

And then like a thunderclap, September 5, the news of the massacre of St Bartholomew was brought to the prince, and he knew that the promise of Coligny to conduct 12,000 arquebusiers to the succour of Lewis could not be redeemed.

In this emergency William saw that he must himself endeavour to raise the siege.

He accordingly marched from Flanders and, September 11, encamped at the village of Harmignies, a short distance from Mons.

In the night six hundred Spaniards, each of whom to prevent mistakes wore a white shirt over his armour, surprised the camp.