1. Well, it is not I myself that has come to the conclusion that is possibly, or even probably, the tomb of Atilius A.f. Cn. Calatinus. "PHDiva" discusses this in more detail, here, stating that the portrayal of a crucified man would support the interpretation of the other iconographs within that this indeed is the tomb of that Atilius. And it was not I or she who came to that conclusion initially. She obtained her information from Filippo Canali di Rossi, in his peer-reviewed article in Italian, Il sepolcro di Atilio Calatino presso la porta Esquilina. And the Italian scholar appears to be quite certain that this is his tomb.
Now, whether this portrayed suspended subject was Marcus Atilius Regulus specifically would be very impossible to prove, particulary when at about that time, one Carthaginian General Hannibal Giso was also crucified in 257 BCE: (Livy, Periochae 17:6) Hannibal, dux Poenorum, victa classe cui praefuerat, a militibus suis in crucem sublatus est. (Hannibal, the Carthaginian general, was hoisted onto the stake* by his men after the navy he commanded had been defeated.)
* Livius.org simply has "crucified," which means, nail to a cross or tropaeum. I am assuming an impaling stake here.
What compounds the problem is that the ancient Latin writers speak of different tortures that killed marcus Atilius Regulus.
Valerius Maximus IV.4.5-6 does not mention how he died, just that he in turn "suffered glory and misery" and that he had disappeared. (Latin)
Seneca Epistles 98.12: Dic tibi: 'Ex istis, quae terribilia videntur, nihil est invictum. Singula vincere iam multi: ignem Mucius, crucem Regulus, venenum Socrates, exilium Rutilius, mortem ferro adactum Cato; et nos vincamus aliquid.' (Say for yourself: "Because of these, what terrible sights are seen, not one is invincible. Many men have already defeated them one by one: Mucius the fire, Regulus the crux, Socrates poison, Rutilius exile, Cato the stabbing death by iron; and to some degree we may defeat them."
Seneca is far too laconic for us to determine whether by crux, he meant a cross, impaling stake, or something else entirely.
Cicero In Pisonem 43 : nec mihi ille M. Regulus quem Carthaginiensis resectis palpebris inligatum in machina vigilando necaverunt supplicio videtur adfectus. (Nor does that illustrious man whom the Carthaginians, having cut off his eyelids and bound him in a machine, killed by keeping him awake, appear to have had punishment inflicted upon him.) Link for Latin text.
Here, Cicero doesn't mention anything of any cross. He just said that Regulus was bound inside some kind of machine or device that kept him awake.
Silius Italicus Punica II.340-4: vidi ego, cum, geminas artis post terga catenis eiunctus palmas, vulgo traheretur ouante carceris in tenebras spes et fiducia gentis Regulus Hectoreae; vidi, cum robore pendens Hesperiam cruce sublimis spectaret ab alta. (I saw, when both hands bound behind his back with tight fetters, before the rejoicing masses Regulus of Hector the hope and courage of the [Roman] people was dragged into the darknesses of prison. I saw when hanging from the oak, raised on high, he saw Hesperia [that is, Italy] from his lofty crux.
Again, Silius Italicus does not specify what kind of crux. Everybody thinks "cross," but it could have been something different. The oak (robore) Regulus reportedly hanged from could be a timber (beam), a post, a trunk, or even a live tree.
Florus Epitome I.18.25: Sed nec illo voluntario as hostis suos reditu nec ultimo sive carceris seu crucis supplicio deformata maiestas; immo his omnibus admirabilior quid aliud quam victor dr victoribus atque etiam, quia carthago non cesserat, de fortuna triumphavit? (His voluntary return to his enemies and his final sufferings, whether in prison or on the crux, in no way sullied his dignity; nay rendered by all this only the more worthy of admiration, what did he do but triumph victorious over his victors and, since Carthage had not yielded, over Fortune herself?) Link to Latin text.
The link has crux translated "cross" which, again, could mean something else entirely. Silius Italicus has him hanging from an oak!
Zonaras quotes Cassius Dio (Roman History Bk. 11 [at bottom of webpage]) as writing, "And he was tortured to death, as the report goes, by his captors. They cut off his eyelids and for a time shut him up in darkness, then they cast him into some kind of specially constructed receptacle bristling with spikes, and made him face the sun; thus through suffering and sleeplessness -- for the spikes kept him from reclining in any fashion -- he perished. When the romans found it out, they delivered the foremost captives in their hands to his children to torture and put to death in revenge."
No mention of any cross or crucifixion. just a swarm of iron spikes that would pierce him if he reclined in any way. And it turns out, it is these, that Tertullian called "so many cruces!"
Tertullian, ad Nationes I.18.10: Si crucem, configendi corporis machinam nullus adhuc ex vobis Regulus pepigit,... (If the crux, the siege-engine of the body that is about to be transfixed [or subjoined], thus far not a one of you all save Regulus has agreed upon...)
Tertullian, ad Nationes I.18.3: Crucis vero novitatem numerosae abstrusae Regulus vester libenter dedicavit. (Your Regulus gladly initiated the novelty of the crux: numerous and driven in.)
Tertullian, ad Martyres 4.6: Regulus, dux Romanorum, captus a Carthaginensibus,... hostibus reddit et in arcae genus stipatus undique extrinsecus clavis transfixus, tot cruces sensit! (Regulus, a general of the Romans, captured by the Carthaginians,... he returns to the enemy and, crammed into a sort of strong-box and transfixed with nails, he felt so many cruces!)
From Tertullian, we find that the crux was, in general, a siege-engine of the body; and specifically for Regulus, there was a novelty to the crux: there were many of them, numerous and driven into a strong-box! So what sort of crux he suffered was not necessarily a cross, but a torture by and inside a sort of "iron maiden," a receptacle for his body that was bristling like a porcupine, but on the inside, with innumerable "cruces:" impaling spikes.
But it still does not deny the fact that there is, portrayed in the tomb, a man bound at the wrists and suspended from an overhead beam. Whether this was intended to portray Regulus or someone else who was hanged by the Carthaginians, we do not know, for the ancient reports conflict with the modern idea that Regulus was nailed to a cross or even a post! Those reports that appear to confirm modern thought,
End of point 1. (cont. for point 2, etc.)
