A hill in Yorkshire, thought to have been a Norman castle motte, is in fact an Iron Age monument, built by hand 2,500 years ago. Skipsea Castle in Yorkshire is not, as previously thought, a Norman motte and bailey castle but is an Iron Age monument more similar to Silbury Hill in Wiltshire .

The discovery makes Skipsea Castle almost unique in Britain. The closest mound of a similar size in continental Europe is the Celtic fortified site of Heueneberg, overlooking the Danube River in Baden-Württemberg.

The discovery of an Iron Age monument hiding in plain sight has taken archaeologists by surprise, since everyone had assumed that it was one of the many castle mottes to be constructed by the Normans from 1066. The huge size of castle mottes means it is far too expensive to excavate them and so there is not a great deal of evidence from the ground to set against educated guesses and suppositions.

It shows how easy it is to make a mistake in archaeology when the basic work of excavation is too expensive or difficult. I still think about my excitement at seeing a previously uncharted mound with a nearby (rather imperfect) stone circle in old Oxfordshire woods near Cholsey, only to be told that the mound was what remained of the old cricket pavilion that burned down in the 1960s and the stone circle was just forgotten builder’s rubble dumped illegally from the same period.

The Skipsea discovery was made using a radiocarbon technique showing that the mound was already 1,500 years old at the time of the Norman Conquest. To recover dateable material, the archaeologists drilled small boreholes through each mound from the top to the base, like coring an apple. These boreholes provided a complete picture of the interior of the mounds with minimum disruption.

From tiny pieces of evidence, such as charred seeds or pollen, the archaeologists could reconstruct the environment the mounds were built in, and organic material has been dated to reveal the age of the mottes. The project, entitled “Extending Histories: from medieval mottes to prehistoric round mounds”, is being funded by the Leverhulme Trust. Details of the project and updates can be found at: https://roundmoundsproject.wordpress.com/