P.
Bastien, in
his monograph on
Roman imperial
bust types, devoted a chapter to these
types with the short spears and considered them to be assimilations of the emperors to Veiovis/Jupiter, because according to Aulus Gellius the statue of Veiovis in
his temple on the Capitoline
Hill showed the god holding arrows instead of a
thunderbolt.
The correct explanation of this
bust type, however, seems to have been discovered by Sylviane
Estiot in her article "Sine arcu sagittae: la représentation
numismatique de plumbatae / mattiobarbuli aux IIIe-IVe siècles (279-307 de n.e.)",
Numismatische Zeitschrift 116/117, 2008, pp. 177-201.
According to
Estiot, the short spears held by the emperors in these
bust types were actually a weapon that was used by
Roman legionary soldiers of the period, namely a short spear weighted with lead that was meant to be hurled by hand and was called a "plumbata" or "mattiobarbulus".
The proof is, in the first place, the following passage of Vegetius, De re militari, 1.17:
"Young
men should also be taught how to use plumbatae, which are also called mattiobarbuli. Two legions in Illyricum, comprising six thousand soldiers each, once wielded these
weapons with such skill and
courage that the
men themselves were called mattiobarbuli. These legions were so successful at winning battle after battle that
Diocletian and
Maximian, upon becoming emperors, ordained that as a reward for their valor these mattiobarbuli should assume the epithets 'Jovian' and 'Herculean' and that they should be considered the
crack troops of the army. Each soldier normally carried five mattiobarbuli attached to
his shield, and, if they threw them effectively, these shield-bearing footsoldiers could virtually fulfill the role of archers. For they could inflict severe damage to enemy soldiers and their horses before it came to hand-to-hand fighting, indeed while the enemy was
still outside the range of javelins." (my translation from the Latin)
According to Vegetius, two Illyrian legions were particularly adept at using this weapon. This fits with the facts (1) that the surviving examples of these short spears, their points and lead
weights since their wooden shafts have perished, have been found predominantly in Croatia,
Austria, and
Hungary, and (2) that three of the four mints that used the
bust types in question, namely
Ticinum,
Aquileia, and
Siscia, are also in or adjacent to
Pannonia (see map,
Estiot p. 201).
The surviving plumbatae have bulges of lead in their shafts, apparently to increase their
weight and penetrating power: see the four examples illustrated by
Estiot, p. 200. According to
Estiot (it's not entirely clear in the pictures), two of the short spears held by
Maximianus on the
aureus shown above, enlarged by
Estiot on p. 196, also have bulges in their shafts, just at the point where the emperor is grasping them with
his hands.
The second
bust type above shows short spears inserted in the respective emperor's
shield, exactly as Vegetius describes. There can be little doubt,
Estiot suggests, that Diocletian's and Maximian's use of this
bust type, 1b and 2c above, commemorated their honoring of the two legions who
had become particularly effective in the use of this weapon, as Vegetius relates.
Estiot thinks Vegetius is exaggerating when he asserts that these short spears could inflict damage at even longer range than javelins.
Bust type 2, after all, shows the emperor holding a normal spear in
his right hand, which he would certainly have to throw before reaching for the short spears attached to
his shield! So the short spears will have been effective at middle range: first the soldiers hurled their long spears, then they threw the short spears attached to their shields, and finally they drew their swords and fought hand to hand.
Modern attempts to reconstruct and throw these short spears have shown that they could travel about 60 meters (66 yards) and could be launched most effectively with an underarm throw. On p. 200
Estiot shows a modern "
legionary" in the
act of hurling one!
It would appear from the Aquileian folles, 2e above, that
Severus II used some troops armed with these short spears for
his invasion of
Italy against
Maxentius in 307.
Estiot suggests that it may have been the sorry
fate of this expedition, with
Severus captured and executed and many soldiers deserting to
Maxentius, that explains the disappearance of this weapon from the coinage at this juncture!