Edwin next moved against Wales: he invaded the Welsh north and captured Anglesey. He drove Cadwallon to the far eastern part of the island and laid siege to him at Priestholme. This caused Cadwallon, a Christian king, to ally himself with Penda, the pagan king of Mercia. Cadwallon's motive was revenge on the powerful Northumbrian ruler who had invaded his kingdom. Penda resented Northumbria's being Christianized by Kent. He also wanted Edwin's power over the other kingdoms.