The earthwork was constructed some time between the
end of Roman rule in Britain in the early 5th century and the
Norman conquest in 1066. Its original purpose is unclear, but it may have been used as a defensive fortification or as an administrative boundary. It possibly marked a 7th-century boundary for the expansionist
Anglo-Saxons, or it may have been a late 8th or early 9th century boundary marker between the kingdoms of
Mercia and
Northumbria. In the
early medieval period, the Anglo-Saxon kingdoms of Northumbria, Mercia, and
Wessex struggled for control over
North West England, along with the
Britons and the
Danes. Whatever its earlier use, the ditch has been used as a boundary since at least the
Middle Ages. Legend has it that Nico Ditch was completed in a single night by the inhabitants of Manchester, as a protection against Viking invaders in 869–870; Manchester may have been
sacked by the Danes in 870. It was said that each man had an allocated area to construct, and was required to dig his section of the ditch and build a bank equal to his own height. but the idea has been dismissed by historians as a "popular fancy". The names derive from "dirty farmstead" and "reedy ditch," respectively.
Antiquarians and historians have been interested in the ditch since the 19th century, but much of its course has been built over. Between 1990 and 1997, the University of Manchester Archaeological Unit excavated sections of the ditch in Denton, Reddish, Levenshulme, and Platt Fields, in an attempt to determine its age and purpose. Although no date was established for the ditch's construction, the investigations revealed that the bank to the north of the ditch is of 20th century origin. Together with the ditch's profile, which is U-shaped rather than the V-shape typically used in military ditches and defenses, this suggests that the purpose of the earthwork was to mark a territorial boundary. ==Preservation==