of the cantref and had secured submissions from the local nobility. To consolidate these gains, Ralph ordered the "strengthening" of a "castle in Maelienydd" in 1242, which in his absence was undertaken in the name of his young son Roger Mortimer. This work is identified with the north-eastern castle at Castle Bank; "strengthening" () may imply the reconstruction of an existing castle in stone, particularly as the establishment of a castle at Cefnllys is not explicitly recorded. Subsequent primary source references to Cefnllys describe it as the "new castle". Upon Ralph's death in 1246, Cefnllys Castle is listed in a patent roll as passing into the custodianship of the crown until Roger's coming of age. Starting in 1256, a large Welsh uprising led by Llywelyn ap Gruffudd, the new prince of Gwynedd, caused an English military reversal across Wales. By the time a truce was signed in 1260, Cefnllys had become Roger's most advanced outpost following the loss of the neighbouring commote of Gwrtheyrnion and the castle at Builth. In late November 1262, Cefnllys was seized from Roger's constable Hywel ap Meurig by a small band of Welshmen, who entered the castle "by treachery" and took Hywel and his family captive, before sending word to Llywelyn of their success and torching the castle. In response, Roger Mortimer levied an army of Marcher lords and arrived at Cefnllys to start repairs on the walls, but was caught off guard when Llywelyn surrounded him with a larger force. After a three-week siege within the damaged and unprovisioned castle, during which Llywelyn's soldiers sacked Roger's other castles at Bleddfa and Knucklas, Roger was forced to negotiate safe passage. Llywelyn allowed the Marcher force to retreat, a chivalrous gesture probably designed to strengthen his case at future peace negotiations, before destroying the remaining defences and continuing his campaign against England. The impact of Cefnllys' fall is illustrated in a letter written to Henry III by Peter of Aigueblanche, bishop of Hereford, as he fled for Gloucester: "Mortimer's castle of Cefnllys has capitulated: Roger and his retinue have left unharmed. All this has led to rumours of treachery and the whole March is in terror." The peace signed at the Treaty of Montgomery in September 1267 was a major success for Llywelyn, granting him formal recognition as Prince of Wales. Even though Cefnllys remained outside of his direct control and Roger Mortimer was permitted to