After 830, Egbert had followed a policy of maintaining good relations with Mercia, and this was continued by Æthelwulf when he became king. London was traditionally a Mercian town, but in the 830s it was under West Saxon control; soon after Æthelwulf's accession it reverted to Mercian control. King Wiglaf of Mercia died in 839 and his successor, Berhtwulf, revived the Mercian mint in London; the two kingdoms appear to have struck a joint issue in the mid-840s, possibly indicating West Saxon help in reviving Mercian coinage, and showing the friendly relations between the two powers. Berkshire was still Mercian in 844, but by 849 it was part of Wessex, as Alfred was born in that year at the West Saxon royal estate in Wantage, then in Berkshire. However, the local Mercian ealdorman, also called Æthelwulf, retained his position under the West Saxon kings. Berhtwulf died in 852 and cooperation with Wessex continued under Burgred, his successor as King of Mercia, who married Æthelwulf's daughter Æthelswith in 853. In the same year Æthelwulf assisted Burgred in a successful attack on Wales to restore the traditional Mercian hegemony over the Welsh.