Sieges were every bit as important as battle in the Civil Wars: many casualties were caused, and much of the cost of the war was absorbed in defending and attacking towns and castles. Holding cities dominated trade, allowed regulation of taxation, and controlled major route ways – thus shaping campaigns. Many battles occurred when, and where, they did because armies were deployed to capture or relieve towns and were confronted en route to their objective. Moreover at any given moment until the final stages of the First Civil War, roughly ten times as much ordnance was tied up in static defences around the country as was actually in the field as part of ‘marching trains’ of artillery. Though it would be wrong to say that sieges of the Civil War were stereotypical, there were methods of reducing fortresses which were widely employed and commonly understood. These were often patterned on long practised continental methods. Many sieges therefore tended to follow a series of recognisable phases. The artillery had a particularly significant role to play in determining whether sieges were possible, the timing and importance of each phase of a siege – and indeed ultimate success or failure. Similarly there were customs of war that were generally expected to be adhered to, and were often referred to as ‘laws of war’ – even if these rules were not exactly codified, nor ratified by explicit convention. Again the artillery played a crucial part in what could be expected from those attacking or defending.

Most sieges began with the appearance of a detachment from a hostile army near a town or castle. Usually those about to be besieged would now be offered the chance to surrender, or to change sides. An emissary would approach the gates accompanied by a drummer, and perhaps a flag of truce.