A Theory on "PILA MURALIS"
As far as we know, no one really knows what the true idea is, in the strange pointy wooden stakes, commonly called PILA MURALIS ”Wall Spears”.
In ”Roman Military Equipment” M.C. Bishop clearly states, that ”PILUM MURALIS” according to roman writers, was a heavy defence spear (Pict. 1) used to throw at the enemy from the top of city walls, and not a rampart stake for building march camp defences. So actually, we do not know what the Romans themselves called these stakes, maby ”Sudes?” or ”Valles?”.
In Polybius (c. 200 – c. 118 BC) “Historia” (Book 18 p123) we are told that making a Vallum round a march camp reinforced with wooden stakes, is something the Romans learned from the Greeks. The Greeks however would cut their stakes on site, choosing trees with branches that could be interlaced when making a fence. The Romans had their stakes cut in advance, mostly from oak, and they carried these with them. Three or four a man.
Appearantly also the roman stakes have – here 200 BC – brances. They have not yet become the doublepointet stakes we know from first century AD finds.
There apparently are no, neither written or pictorial description of these stakes in the first century sources or later. And so, we actually have no ”original Roman record” to what we should do with them. Only the archaeological finds.
It's impossible to get a complete record on the finds of "PILA MURALIS". These ”low interest” items are not the most common talk on Google or in books on The Roman March Camp. But on the few one can find, there is some very interesting features though. The two finds I found are both from Germany. One is from Oberaden – illustrated in "Roman Military Equipment", the other is from Aalen (Pict 2.). The stake from Oberaden has a Centurial inscription cut on its side that tell, that this stake belongs to ”I cent V Coh (?)”. It confirms the theory, that these stakes was not made on site, but a part of the general legionary camp equipment that was carried, when on march.
The stakes from Aalen is of three very different sizes and forms, telling us that the stakes was made by different persons, probably legionnaries – not to follow fixed standard mesures – but to follow standard idea; the two pointed ends and the narrow ”grip” in the center.
There has been many discussions through the years as to how to use these stakes. A common way of use is binding them in sets of three as a giant caltrop, a ”Tribuli” (Pict 3). It has also been suggested that they could be used as a kind of fence, made from the stakes crossed and supporting a long bar, and so making an ”cheveaux de frise”” – an ”Ericus” as the Romans called it. This is a very credible theory. One of the basic drills for Roman legionnaries was to make a ”Murum” a defensive wall with shields in a double row. When a Murum is made with Pilas - the legionary javelins - they would stick out from the shield-wall like a ”hegdehog” – an ”Ericus” – wich would effectively stop f.inst a cavalry attack. So would using the Vallum stakes this way also. Horses would hate them.
Most commonly they are used by reenactors as palisade stakes placed on top of the earthwork – the ”Agger” behind the ditch, the ”Fossa”. When placed like this they are often tied together with a rope as a light fence.
But as any renactor know, this have no defensive value at all. If you storm the ditch, you can easily jump over the fossa and kick down the stakes, even if they are buried quite deep in the agger. They are – used like this – only a visual defence.
Our theory on trial
In our trial we asked ourselves; Why do they look the way they do - even with the major indifferences the achaeological finds show?. What is the idea with the dual pointy ends? Why is there a sort of ”grip” a short narrow handle in the middle?
If you carry these stakes with you as a part of the basic marchcamp equipment, they must have had som sort of vital defensive or regulating purpose. Not just as a nice decorative fence. No doubt that the idea of using them for an ”Ericus” makes sense. But they must also have been used as a part of the camp defence – the Vallum; the Fossa and the Agger.
And if so, they must have had some defensive value – not only as a fence but as a real useful obstacle that would hinter an enemy to cross the camp perimeter.
So this is what we did; We tied the stakes together as crosses. Then we dug them into the Vallum, so they would be a real part of the dirtwork structure. The Peat or Turf that we cut out when we started digging the fossa, we used to reinforce the front of the vallum with the stakes.
This meant, that we got a very tough fortification. The ”Valles” (Stakes) now could not be overturned, and they gave true defensive value. They made it very difficult – and unpleasant thanks to the pointy ends on the stakes - to cross the Fossa. That we tied the Valles together meant, that pressure on one part of the stake created a counterpressure in parts of the stakes that were dug down. We found, that this way of using the ”VALLES”, were very credible.
Read Polybius on Vallum Stakes yourself at: