On 14 April 1643, Robert Devereux, 3rd Earl of Essex led a Parliamentarian army of 19,000 troops to lay siege to the town, and began bombarding it two days later.

In August 1642, King Charles I raised his royal standard in Nottingham and declared the Earl of Essex, and by extension Parliament, to be traitors, marking the start of the First English Civil War.

[3] After being repelled from London, he retired back through Reading, where he left a Royalist garrison of 2,000 soldiers under Sir Arthur Aston, who was appointed as governor.

Over the winter months, Aston oversaw the creation of a defensive line; a ditch with a raised earthen rampart linking a series of bastions.

[14][15] The Parliamentarians held a council of war, in which Essex sought advice on whether to attempt to storm the town, or to be more cautious and lay siege to it.

Essex agreed to be cautious, aware that he could not afford to lose many men, as he would need them for his planned subsequent attack on Oxford.

[19] Two days later, around 700 Royalist musketeers commanded by Lieutenant General Wilmot managed to reinforce Reading via Sonning, to the east of the town.

The Royalist historian, Edward Hyde, 1st Earl of Clarendon suggested that the affliction might not have been genuine, but rather a way of maintaining his reputation in a lost cause.

The same day, a relief force commanded by King Charles and Prince Rupert attacked the Parliamentarian army at Caversham Bridge, but Feilding held to the truce, and the garrison did not join the battle.

[23] Feilding negotiated generous terms of surrender; he and his men were granted safe passage to Oxford with flying colours.

[26] The capture of Reading meant the Parliamentarians could challenge Oxford directly, but Essex and William Waller were unable to coordinate their forces for an attack.