The Siege of Colchester commenced in June 1648 as Parliamentarian forces, led by Sir Thomas Fairfax and Oliver Cromwell, targeted the last significant Royalist stronghold in Essex. The Royalists, numbering around 3,000 troops under the command of Sir Charles Lucas, expected to hold the city against a larger enemy force. For over eleven weeks, the siege inflicted considerable hardship on the defenders, exacerbated by dwindling supplies and constant bombardment from Parliamentarian artillery. Residents and soldiers alike endured severe scarcity of food and resources, while the Parliamentarian blockade restricted any potential reinforcements from reaching the besieged city.

As the siege progressed, the conditions within Colchester deteriorated. The Parliamentarian troops eventually adopted more aggressive tactics, leading to the final assault that forced the Royalists to surrender. On August 28, 1648, Sir Charles Lucas formally capitulated, marking a significant point in the conflict. The surrender effectively shattered Royalist hopes of a resurgence and solidified Parliamentarian control in the region. The aftermath of the siege included the execution of Sir Charles Lucas and Sir George Lisle, who were found guilty of treason, further demoralizing Royalist supporters.