In 1980 E.P.Thompson published an interesting paper called *Barbarian Invaders and Roman Collaborators *. Among other subjects he consdiers there the leakage from Rome to its enemies of technical knowledge needed to construct and deploy ancient artillery pieces:
But soldiers and others might also give the enemy technical knowledge which had not previously been available to them, especially knowledge of how to construct and use the dreaded Roman artillery, the ballistae of various kinds. When Septimius Severus defeated one of his rivals in 194 numbers of the defeated troops fled to Persia; and some of these men were technicians. They settled down in Persia and not only taught the Persians how to use weapons which they had not used before but also showed them how to make these weapons for themselves. The result was that the Persians had higher hopes of victory now than formerly when they engaged the solid ranks of a Roman army; and the historian who reports this matter looks upon it with grave concern.
However, quite puzzlingly, artillery just didn't quite catch on with the Persians or others, as Thompson himself notes a bit later:
But although we hear of deserters and prisoners handing on this knowledge to the Persians and others, we never hear that the Persians and the others absorbed this skill into their general military techniques, so as to be able to apply it on their own account when there were no obliging prisoners and deserters with them to give them instruction. In spite of what had happened in 194 we never hear in later ages that the Persians could make and use ballistae on their own account. I do not know why this should have been so. Not all ballistae can have been very difficult to make and use, for we possess a letter in which a bishop tells us that he was engaged in making one and proposed to use it. If a bishop could do so, why not Alaric or Attila or their henchmen?
Perhaps with the Huns and other tribes artillery didn't fit into their notions of warfare, but it does seem very strange that the Persians neglected this arm. So I am still puzzled.
Maybe the Persians had a warrior code that precluded widespread use of artillery? (Hard to believe, as they had set so much store by arrows). Or maybe a prosaic lack of good wood is the crux of the matter?
Has the issue been studied by later historians?