According to the Peterborough version of the Anglo-Saxon Chronicle, written in the 12th century, this name was given at the time of the foundation of a monastery there in the 7th century, owing to the presence of a spring called "Medeswæl", meaning "Medes-well".
The earliest reliable occurrence of the name is in Bede's Ecclesiastical History, where it is mentioned in the genitive Latinised form "Medeshamstedi", in a context dateable prior to the mid-670s [REF].