| Conflict: | Siege of Mercq |
| Partof: | the Hundred Years' War |
| Date: | 6 May 1405 |
| Place: | Mercq, Pas-de-Calais, France |
| Result: | English Victory; French attack army routed |
| Combatant1: | Kingdom of France |
| Combatant2: | Kingdom of England |
| Commander1: |
|
| Commander2: | Richard Aston Robert de Berengeville |
| Strength1: | ~800
|
| Strength2: | ~500 |
| Casualties1: | Heavy |
| Casualties2: | Light |
On 6 May of 1405, a French army under the command of Waleran III, Count of Ligny and Saint-Pol besieged the English castle at Mercq in Pas-de-Calais.
The French siege proved futile as English reinforcements under Lieutenant of Calais Sir Richard Aston arrived with the Calais garrison to counterattack and lift the siege. Although surprised by the English attack the French troops manned the trenches, but the Genoese crossbowmen had no bolts and St. Pol's army suffered losses from English archers. The first to flee were the Flemings, quickly followed by the French and Genoese. Waleran III escaped with remnants of his army, but most were either killed or captured. The English captured all the French artillery, four standards, 60-80 prisoners including Jean de Hangest.