Siege of Gloucester The Siege of Gloucester was an engagement in the First English Civil War . It took place between 3 August and 5 September 1643 , between the defending Parliamentarian garrison of Gloucester and the besieging army of King Charles I . The siege ended with the arrival of a relieving Parliamentarian army under the Earl of Essex . The Royalist forces withdrew , having sustained heavy casualties and had several cannon disabled as a result of sallies made by the defenders . Prelude . The siege took place after a run of Royalist successes , known as the " Royalist summer " . After the fall of Cirencester , Gloucester was one of the few remaining Parliamentarian strongholds in the west . During a council of war at Bristol , the King faced a decision to either attack a weakened London , or to consolidate the South Western Royalist stronghold by attacking the small garrison at Gloucester . Although the reasons for his decision are not known , Gloucester ' s position cutting the overland route between Royalist - held Wales and Cornwall made it a favourable target , and with the city having only a very small garrison the King may have believed that Gloucester would fall quickly . Five days before the arrival of the Royalist army the defenders had discovered they were to be attacked and messengers were sent to London to ask Parliament for assistance . The Siege . On 10 August , the Royalist Army arrived at Gloucester and promptly demanded that Colonel Edward Massey surrender . Massey refused and Royalist forces began digging in and setting up artillery batteries around the South and East gates of the city and also severed or diverted water pipes . The defenders burned houses and other obstacles outside the city walls . The bombardment of the city began . However , over the next days , the defenders made several sallies from the gates , attacking and disabling Royalist artillery , taking prisoners and tools . Breaches in the wall were filled with cannon baskets and wool sacks . The Royalists made attempts to drain the city moat and fill it in at places . As the siege was prolonged , the King himself requested his favourite Prince Rupert , who was currently holding the newly captured port of Bristol , to acquire a newly built cannon from his friends and associates in the Low Countries . This was done post - haste and this huge cannon was shipped over to Bristol and escorted up the Severn Channel to Gloucester , to be positioned just outside the city walls ( actually on the high wall of Llanthony Secunda priory in Hempsted ) , aimed at the Cathedral itself . Unfortunately for the King , his gunners had no experience of firing the brand new gun , especially one larger than they had ever used before , and , on its initial firing , the cannon exploded . With this failure and the excessive time spent trying to take Gloucester , the King had given Parliament enough time to gather huge London forces to march to its relief . On 26 August the Earl of Essex left London with an army of 15 , 000 men to relieve the City . Meanwhile , the Royalist Army began tunnelling to place a mine under the East Gate , but a sudden spell of bad weather flooded the tunnel , leaving enough time for the Earl of Essex to arrive and reinforce the city . By the end of the siege , Colonel Massey had only three barrels of gunpowder left for the defence of the City . Aftermath . With the Arrival of the Earl of Essex , the Royalists forces withdrew and began to march on towards London . They intercepted Essex ' s army at the First Battle of Newbury , but failed to destroy it . For the remainder of the war , Massey ' s force based in Gloucester continually threatened the lines of communication between Oxford , the King ' s wartime capital , and Wales and the West Country . Following the return of Charles II to the throne , the king took his revenge upon the city by having its walls torn down . The foundations of the wall , however , are still visible in parts of the city today . Commemoration . For centuries afterwards , the lifting of the siege was marked by an annual Gloucester Day . This died out in the nineteenth century but was reinstated in 2009 . The modern " Gloucester Day " has recently included a parade by the Mock Mayor of Barton , an office created after Barton was moved outside of the limits of the city following the restoration of Charles II .