The Parliamentarians were inside, and the army of King Charles 1 were outside.

The Siege of Gloucester took place during the First English Civil War. It took place between 10 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.

[See Wikipedia] (https://en.wikipedia.org/wiki/Siege_of_Gloucester)