 The Mercians, who participated in Edwin's defeat in 633, seem to have presented an obstacle to Oswald's authority south of the Humber, although it has been generally thought that Oswald dominated Mercia to some degree after Heavenfield. It may have been to appease Oswald that Penda had Eadfrith, a captured son of Edwin (and thus a dynastic rival of Oswald), killed, although it is also possible that Penda had his own motives for the killing.
