The destruction of the Royalist field armies at Naseby and Langport in 1645 did not end the English Civil War. Althought the king had suffered irreversible military defeats, Parliament was unable to govern effectively while politically important towns and fortresses remained in enemy hands. To ensure political stability Parliament’s army was forced to besiege and reduce a large number of strongholds in England, Ireland and Scotland, a task that was not finally completed until the surrender of Galway in 1652. In particular the war in Ireland was to test the army’s siege-making capacity more severely than any previous campaign. To complete the political conquest of Britain and Ireland the army and its generals were compelled increasingly to practise an aspect of warfare that had been traditionally neglected by English soldiers. In contrast, siege warfare was an area in which their continental counterparts had excelled.
In the sixteenth and seventeenth centuries, European wars produced few set-piece battles. Conflicts were more frequently resolved by the assault and defence of fortified cities and towns. Consequently the art of siege warfare evolved rapidly. England’s political and military insularity during this period detached the country from advances in siege technology that had transformed the conduct of European warfare. No major siege had been undertaken by an English army since Henry VIII had invested Boulogne in 1544, and as there had been no siege of English towns or fortresses since medieval times, there had been little innovation in defensive fortifications. What improvements did occur were sporadic and unco-ordinated. In the sixteenth century a great fortress was built at Berwick-on-Tweed to counter Scottish infiltration and a number of coastal towns in the south-east were refortified against the threat of Spanish invasion. However, by the outbreak of civil war in 1642, even these were obsolete by contemporary continental standards.