The retreat of Guthrum and his band to East Anglia in late 879 and the similar retreat of the Viking army stationed at Fulham, west of London, back to the Continent at the same time (both events recorded in the "Anglo-Saxon Chronicle"), can be seen as a tactical response to the effectiveness of the strategic offensive posed by the construction of the Burghal system. The ratification of a mutually agreed boundary to the east of London, in Alfred and Guthrum's Treaty, between Guthrum's new Viking kingdom of East Anglia and Alfred's newly won territory, can best be ascribed to this time. These developments gave Alfred control of London and its surrounding territory, which included a good length of the strategically important Watling Street as it approached London. This interpretation is supported by the issue at this time of the special celebratory London Monogram coinage from the London mint, now under the control of Alfred, and by the issue at the same time of coins from Oxford and Gloucester in southern Mercia.