Hadrian's Wall - the Vallum

One aspect of the Hadrian's Wall had puzzled us for some time. There are sections of the wall where the ditch is on the South side. But surely it should be to the North as the Romans were defending against the Celtic tribes.

The answer is, as usual with the Romans, simple but with underlying complexities. The Wall was designed not just to keep out the tribes from the North but also to separate them from their allies to the South.Basically the Romans wanted to create a military zone , looking both South as well as North. As an added advantage it would also help to keep their stores and provisions safe.

One small point, we call the ditch to the South of the Wall a Vallum, but really it is a Fossa.

Size of the Vallum? Well Alastair Moffat in his book on the Wall says

1. 5.4 to 5.9 metres across the top
2. Depth of between 2.6 and 2.9 metres.
3. 2.1 m across at the bottom.

Basically it was designed for steep, 60 degree slopes . The soil and rubble dug out was moved away from the Vallum to avoid infill and was used to create braod berms of 9 to 12 metres in width.

Over time it is probable that the vallum filled up with water to present an even more formidable obstacle.