Background

Ambrogio Spinola had captured Oldenzaal in 1605 and Groenlo a year later – with this the region was under Spanish occupation and they undertook raids. In May 1626, the Dutch decided to eliminate the Spanish from the area once and for all. They brought two armies under the command of Frederick Henry, Prince of Orange and with them a detachment of the English army which had been raised as result of their war with Spain.^[1] Oldenzaal's garrison which had been continuously strengthened since it capture and twenty years later the city had around 800 troops along with cannon under the command of Spanish Governor Guillermo Verdugo.^[5]

Siege

On July 23 the Dutch and English besieged the town and had a good view of the surrounding environment; as a result, Casimir did not find it necessary to construct a circumvallation line against a possible Spanish relief attempt. Casimir with skilled pioneers dug siege lines with trenches, and batteries were put into position. A few companies of English were detached against Broeckhuise castle on the outskirts which posed a threat but it was captured within two days.^[1] It was subsequently plundered and burnt by Dutch troops.^[6]

The canals of Oldenzaal were controlled by two sluice gates. Casimir ordered his batteries to fire on the gates which eventually collapsed and the water from the canals was drained. The besieged were now cut off and having realized there was no hope of a relief, Verdugo asked the Anglo-Dutch for terms.^[7] After a mere ten day bombardment there was an honourable end to the siege; Verdugo surrendered the city and marched out under the honours of war.^[2]

Aftermath

Casimir made a triumphant entry into the city - Protestants defectors were soon arrested. Oldenzaal was a strategic place for the republic and the fortress walls despite the protests of the city burghers were demolished. However, parts of the old medieval remained, the city wall and parts of the canals were maintained in order to defend against mutinous troops. The following year Groenlo was taken in a two month siege.^[4]