The siege of Ostend was a three-year siege of the city of Ostend during the Eighty Years' War and the Anglo–Spanish War. A Spanish force under Archduke Albrecht besieged the fortress being held initially by a Dutch force which was reinforced by English troops under Francis Vere, who became the town's governor. It was said "the Spanish assailed the unassailable; the Dutch defended the indefensible." The commitment of both sides in the dispute over the only Dutch-ruled area in the province of Flanders, made the campaign continue for more than any other during the war. This resulted in one of the longest and bloodiest sieges in world history: more than 100,000 people were killed, wounded, or succumbed to disease during the siege.
Ostend was resupplied via the sea and as a result held out for three years. A garrison did a tour of duty before being replaced by fresh troops, normally 3,000 at a time keeping casualties and disease to a minimum. The siege consisted of a number of assaults by the Spanish, including a massive unsuccessful assault by 10,000 Spanish infantry in January 1602 when governed by Vere.