Pryderi's armies were expected to make up the bulk of Caer Dathyl's defenses. Yet Pryderi had grown scornful of the petty bickering between the cantrev lords under High King Math's rule, and secretly made an alliance with the Death-Lord, believing that his rule offered the only prospect of peace and unity. Pryderi's arrival at Caer Dathyl proved disastrous for the Sons of Don, for though Math's forces under Gwydion had gained advantage and begun to push Pryderi's forces back, Arawn's deathless Cauldron-Born arrived, slew King Math and laid the fortress waste.