The Devil's Dyke is one of the largest ditches in Great Britain. It is 12km long and 4m deep. It also has a 6m high bank (a wall made of earth). It is in Cambridgeshire. It would have taken 200 men about three years to build it! There are (or were) other big ditches nearby called Black Ditches, Fleam Dyke, Brent Ditch & Bran Ditch. For over a century, archaeologists have puzzled over when they were dug.  Roman coins found beneath one show that it was built after they left Britain. Special techniques have dated objects found in others to the 5th or 6th century. This was during the Dark Ages. The Saxon Kings of East Anglia had only just set up their kingdom. The ditches were probably built to keep out the British from Calchfynedd. They showed where the border was. They protected an important road called the Icknield Way. Soldiers posted there could control people going in and out. If they were traders (people selling things), they could make them pay taxes. They could be used to defend the kingdom during a war. The banks & ditches may have been improved in the 7th century. Calchfynedd had been taken over by another Saxon group called the Mercians. Their king, Penda, wanted to rule over East Anglia too. There were lots of bloody battles. The ditches were no match for his mighty army which killed many East Anglian soldiers and 3 Kings. In the 10th century, England became one country. There was lots of arguing about who should be king. Some of King Edward the Elder's relatives wanted to rule instead of him. Edward hunted down one cousin to East Anglia, but he and his friends hid behind the dykes. The Devil's Dyke was then just known as the 'Great Dyke' or 'St. Edmund's Dyke'. It was in Medieval times that people called it the 'Devil's Dyke'. They thought it had been made by his fiery tail as he was chased away from a wedding at nearby Reach Church!  There is a similar big ditch in the South-West called Wansdyke.