 The expansion of Wessex in the tenth century would have caused the obliteration of the Middle Anglia's old divisions, by which time the places listed would have become mere names.Middle Anglia in the 7th century constitutes a model for the development of English administrative units during the period, according to Davies and Vierck, who demonstrate that it was created by Penda of Mercia when he made his son Peada king of the Middle Angles at the time that they were introduced to Christianity.James Campbell refutes suggestions that the hides given for each tribe were the sum of a system of locally collected assessments and argues that a two-tier system of assessment, one for large areas such as kingdoms and a more accurate one for individual estates, may have existed.