Colchester found itself in the thick of the unrest when a Royalist army on its way through East Anglia to raise support for the King, was attacked by Lord-General Thomas Fairfax at the head of a Parliamentary force.

The Parliamentarians' initial attack forced the Royalist army to retreat behind the town's walls, but they were unable to bring about victory, so they settled down to a siege.

The Suffolk men were actually more concerned about preventing either side from spreading destruction into their county and in recognition of this Fairfax gave them the task of guarding the bridges across the River Colne to the north and east.

Colchester had been a staunch supporter of Parliament during the First English Civil War and any sympathy with the Royalist army soon vanished as the soldiers seized provisions from the town's people.

The Suffolk men were taken by surprise and were routed; in their enthusiasm, however, the Royalists found themselves too far from the town and were counter-attacked and suffered severe casualties, as well as losing the artillery and provisions they had taken with them.

A detachment of the New Model Army under Colonel Adrian Scroope at St Neots had defeated the Earl of Holland in a night attack.

However, on 22 July, Bernard Gascoigne and his remaining cavalry escaped from Colchester via the Maldon road, fighting a fierce engagement with Parliamentary forces, and headed into Cambridgeshire, where they dispersed.

He received a letter from Langdale, the Northern Royalist army commander, encouraging the Essex men and promising relief within two weeks.

In a last appeal to the humanity of the besiegers, the Royalist commanders sent 500 starving women to the Parliamentarian lines, hoping that they might acquire food by inspiring sympathy.

In celebration, the Parliamentary artillery fired salutes and Fairfax had kites flown into the town carrying news of the destruction of the Royalist army.

A military court found Lucas, Lisle, Farre and Gascoigne guilty of high treason and sentenced them to death by firing squad.

The claims were that Lucas had executed Parliamentary prisoners in cold blood; that he had broken his parole given after the First Civil War; and that the Royalists had continued to fight in an indefensible position, thus causing unnecessary death and suffering.

Within days, pamphlets were produced extolling Lucas and Lisle as martyrs to the Royal cause, and today in the grounds of Colchester Castle there stands a monument marking the site of the execution.

The siege is commonly believed to have inspired the nursery rhyme Humpty Dumpty, which is said to have been the nickname of a large Royalist cannon strategically placed on the wall next to St Mary's Church.

Other stories attribute the name Humpty Dumpty not to a cannon but to a Royalist sniper, "One-Eyed Thompson", who occupied the belfry of St Mary's Church and was shot down by Parliament forces.