During the siege, a 16 km circumvallation line was made around Grol to prevent the enemy from leaving and to prevent the liberation of the city from outside. Ambrosio Spinola had used a similar technique during the Siege of Breda (1624), and after the successful siege of Grol Frederic-Henry would later use it in other sieges in the Netherlands, such as at the Siege of 's-Hertogenbosch. The success at Grol provided the first serious victory on land for the Republic after the Twelve Years' Truce.