I actually recently posted about this Armatura on my Facebook Gladiator research group;
https://www.facebook.com/groups/16304645...397080011/
For those not on FB;
The Dimachaerus is one of the most enigmatic Armatura, only surpassed by the Crupellarius.
Both have in common, that no iconographic evidence can be attributed to these Armaturae, but the Dimachaerus at least is listed together with other known Armaturae in the Onirocriticon by Artemidorus Daldianus.
By this we can be sure that this Armatura was present in the 2nd century AD and had some commonalities with the Armatura of the Arbelas, as Artemidorus seems to consider them interchangeable concerning his divination.
Still, as he takes care to state both names, they would have been considered different Armaturae, their main similarity being that they would have fought with a weapon in each hand, as opposed to a weapon and shield combination or a two-handed weapon like the Retiarius.
Previously it was assumed that the Dimachaerus would have fought with two Gladii of the shorter variant used by the Gladiators, as some reliefs show Gladiators holding a straight blade in each hand.
However it is also clear, that in these reliefs the victor is holding the weapon of the defeated Gladiator in addition to his own, so these cannot be considered as depicting a Dimachaerus.
On the other hand, there is a single relief showing a Gladiator with a curved blade in the left hand and another blade, its shape hidden behind the helmet in his right.
The padded Manica worn on both lower arms, suggest he is supposed to fight with two weapons as opposed to the reliefs mentioned above.
His helmet, upper body covered by a Tunica or Lorica Hamata and his two short greaves are very similar two depictions of Arbeloi dueling each other, so it is very likely, that this actually is supposed to show a Dimachaerus.
Still the question remains what shape his second weapon is supposed to be and which Armatura he would have been paired with.
Concerning his weapons it is noteworthy that the name of the Armatura used by Artemidorus as well as seen in the two Epigrams from Pompeii and Lyon is Greek and not Latin, just like the Arbelas.
Especially the word "Machaera" - a word used to describe a knife more frequently than a sword. This is also true for the word Sica in Latin, both words stressing the cutting action of the respective blade.
As we see in the aforementioned relief, at least one of the weapons wielded is very similar to the curved knife or Sica shown in Use by the Thraces.
The Thracian curved knife or sword the gladiatorial Sica is based on, was also sometimes called Makheira by the Greeks.
Considering this and the translation of the preposition "Di-" as double or dual it would make very good sense to also assume the second blade to be a Sica, even though only the straight base of the blade is visible in the relief.
If one prefers to read "Machaera" simply in the general meaning of a sword or dagger and considers the "Di-" to mean "two of a kind" instead of "to of the same kind" then a short Gladius in the right hand would also make sense, as this would mirror the weapons used by the Arbelas, only exchanging the halve moon blade on the left with a Sica.
Concerning the pairing, multiple possibilities exist.
An epigram from Pompeii announces two pairings of a Dimachaerus against an Hoplomachus, though this reading seems to be very uncertain, according to Junkelmann.
A gravestone from Lyon only tells us that the Gladiator Hylas had fought 7 combats, fighting as a Dimachaerus as well as an Essedarius, and that he was awarded the rudis. Since Essedarii would only fight amongst tmeselves this might be a hint that Dimachaerii would do so as well, but of course this is pure speculative.
Since the Arbelai depicted in similar gear as the Dimachaerus on the relief are solely fighting against each other, a pairing with another Dimachaerus or an Arbelas would seem to be quite feasible.
References:
3rd or 4th century relief from Hierapolis showing what is most likely a Dimachaerus:
https://www.flickr.com/…/4006…/galleries...760254922/…
https://www.flickr.com/…/4006…/galleries...000186711/…
Contemporary relief also from Hierapolis showing two similarly equiped Arbelai:
https://www.flickr.com/…/4006…/galleries...760254922/…
3rd century relief from Ephesos depicting a curved Sica that looks very similar to the weapon of the Dimachaerus relief:
https://www.flickr.com/…/4006…/galleries...760254922/…
https://www.flickr.com/…/4006…/galleries...093765400/…
Reliefs showing victorious Gladiators holding the adversaries weapon (no Dimachaerii):
https://www.flickr.com/…/4006…/galleries...572518239/…
http://media3.s-nbcnews.com/…/_…/gladiat...id-4x2.jpg
BTW, this should be moved to the ancient combat sports section