It runs for 11 kilometres (6.8 mi) in an almost straight line from Reach to Woodditton, with a 10-metre-high (33 ft) ditch and bank system facing southwestwards, blocking the open chalkland between the marshy fens to the north and the formerly wooded hills to the south.

The highest point along the Devil's Dyke is at Gallows Hill, where it measures 10.5 metres (34 ft) from the bottom of the ditch to the top of the earth wall.

From Reach, the dyke crosses farmland, before running along the edge of the July Course at Newmarket Racecourse and then through the woods of a private estate near the village of Woodditton.

The Anglo-Saxon Chronicle may refer to the Devil's Dyke in its annal for 905, when Edward the Elder is recorded as fighting and defeating the Danes of East Anglia, after first laying waste to the countryside: 'and he laid waste their land between the Dyke and the Ouse as far northward as the Fens'—' and oferhergade call hera land betwuh dicun and Wusan.

[7] Abbo of Fleury, writing in the late 10th century, described East Anglia as "fortified in the front with a bank or rampier like unto a huge wall, and with a trench or ditch below in the ground".

[8] The mediaeval Flores Historiarum, referred to "...duo fossata sancti Eadmundi..." – the two fortifications of St Edmund – when describing the battle between Edward and his adversaries.