Castles were normally used to symbolise and exercise control of territory and to safeguard their inhabitants. Rhys Gryg created the castle of Dryslwyn to safeguard his son Maredudd ap Rhys and his inheritance, from the hostile intent of his older brother Rhys Mechyll. Like many other castles Dryslwyn was established at the crossing of routeways: where the road from Llangathen to Llanarthney crosses the River Tywi, by ford or bridge. This enabled it to control traffic on these routes and encouraged economic activity at the site. Following the capture of Dryslwyn in 1287 the castle was garrisoned by 'English' troops. These garrisoned castles of the Tywi valley formed 'the handle' by which the English Crown securely grasped west Wales. During the 14th and 15th century Dryslwyn castle was part of a large complex 'state' supply system. The garrison defended the castle with crossbows supplied from a central castle armoury rather than using traditional personal weapons such as 'long' bows.