Posted this on the Main forum, but once again this feels like it deserves a topic here.
Here is the most complete portion of my Rome imperial collection; an antoninianus from every Crisis era emperor.

Strap your seat belts for a history crash course!
Background:
The Antoninianus is a modern name for a "double denarius" coin introduced by the emperor Caracalla in 215 to inflate the currency supply to stay on top of his exorbitant increases to the salaries of his soldiers. They did not contain a full double amount of silver to match their face value, and were very unpopular. They were produced sporadically until Elagabalus outlawed them, around 220. The semblance of stability vanished in 235 when a general named Maximinus Thrax assasinated Elagabalus' cousin Alexander and began an iron-fisted rule by the military for the military. The Senate hated him, and appointed provincial governors Gordian I and II as co-emperors against Maximinus. They were dead within 36 days. Knowing what he would do upon reaching Rome, they appointed the elderly senators Pupienus and Balbinus as co-emperors again, and Maximinus was killed in a mutiny among his soldiers in 238. Due to the financial stresses of this crisis, Pupienus and Balbinus re-issued the antoninianus. The senators were not popular, and they appointed the 13 year old nephew of Gordian II as co-emperor. This still did not make them popular, and they were dead within two months of Maximinus, leaving the teenaged Gordian III in charge of the whole empire. Under Gordian III the Antoninianus became the dominant silver currency of the empire. Here's were we start.
First row, left to right:
- Gordian III 238-244. Ascended the throne at age 13 and enjoyed a reasonably prosperous rule, mostly as a figurehead while the Senate ran things. Died age 19 while on campaign against the Persians, probably murdered by his own soldiers.
- (missing) Tranquillina, wife of Gordian III. Scarce and expensive.
- Philip I "The Arab" 244-249. Gordian III's praetorian prefect (chief of body guards). Possibly implicated in his death. Rule was marked by numerous usurpers to the throne, and increasingly aggressive raids by barbarians. Died in battle outside of Rome against Trajan Decius over the title of Emperor. Rumored to have secretly converted to Christianity.
- Philip II, Philip's young son appointed co-emperor at age 9 in 247 to establish a line of succession. Stabbed to death in his mother's arms hours after his father's death to establish Decius as the undisputed emperor.
- (missing) Otacilla Severa, wife of Philip I. Retired to obscurity after 249.
- Trajan Decius 249-251. Senator who was placed at the head of an army to defeat a usurper against Philip I. Ironically he was declared emperor immediately after, and marched on Rome as a usurper himself. He defeated Philip and his position was ratified by the Senate. Oversaw especially harsh persecution of Christians. Died along with his son and co-emperor Herennius Etruscus in 251 when a Gothic commander lured his armies into a trap.
- Herennia Etruscilla, wife of Trajan Decius
- (missing) Herennius Etruscus, co-emperor with Trajan Decius. Antoninianii are common, but expensive.
- (missing) Hostilian, younger son and co-emperor with Trebonianus Gallus for two months before dying of plague. All coins are scarce; antoninianii are rare.
- Trebonianus Gallus 251-253. Governor of Moesia under Decius, proclaimed emperor upon the news of the latter's death. Adopted Hostilian as co-emperor, then elevated his son Volusian. Defeated in 253 by another claimant to the throne. Debased the antoninianus from about 40% to under 20% fine.
- Volusian 251-253. Son and co-emperor of Trebonianus Gallus.
- (missing) Aemelian, ruled for 3 months in 253 after defeating Gallus and Volusian. Extremely rare.
Second row:
- Valerian I, 253-258. Censor under Decius, then proclaimed emperor and defeated Aemelian. Debased the antoninianus significantly to about 12% fine. Appointed his son Gallienus as co-emperor in the West so he could focus on the threat of the Sassanian empire in the East. He was summoned to a peace negotiation with Shapur I in 260, but Shapur brought more body guards, killed Valerian's body guards, and took Valerian as prisoner of war. It is said he lived his final years as a slave, with Shapur using him as a human foot stool. After incessant offers of gold for his release, Shapur poured molten gold down the emperor's throat and had him taxidermied.
-(missing) Mariniana, the very scarce wife of Valerian I who died before 253
- Valerian II, 256-258. Oldest son of Gallienus. Appointed caesar and placed in Sirmium (Serbia) under the care of the general Ingenuus. Died about age 15, probably murdered.
- Saloninus, 259-260. Brother of Valerian II. Installed as emperor in Gaul (France) by his father Gallienus around the time of Valerian's capture. Killed by the usurper Postumus.
- Gallienus, 253-268. Son of Valerian I and emperor of a crumbling empire. Under his rule, the border against the Goths was weakened, the entire provinces of Gaul and Syria seceded and became independent empires, and the antoninianus was debased to about 3% fine, and all other denominations were cancelled. Killed in a conspiracy executed by soldiers Claudius and Aurelian.
- Salonina, wife of Gallienus. Reportedly very upset with her husband about their two sons.
- Claudius II "Gothicus" 268-270. Assasinated Gallienus and led a short but very successful rule, repelling a significant Gothic invasion and bringing stability back to the empire. Died of a plague outbreak. Fineness of the antoninianus fell to under 2%.
- Quintillus, 270. Young brother of Claudius II, ruled undisputed for a few weeks or months. Killed himself to avoid civil war with fellow claimant Aurelian.
Row 3: Secessionist empires
- Postumus, 260-269. Created the Gallic empire upon the death of Saloninus. Increased the fineness of the antoninianus significantly. Murdered by his army when he refused to let them sack a city that was harboring a usurper.
-(missing) Marius, a common soldier picked from the crowd to succeed Postumus. Gave the go-ahead to sack Mainz. Said to have ruled for 4 days. Extremely rare.
- Victorinus 269-270. General under Postumus. Murdered by one of his soldiers after getting too friendly with said soldier's wife.
- Tetricus I, 270-274. Governor under Postumus and Victorinus, declared emperor following the death of Victorinus. Said to have happily surrendered power to Aurelian, and was allowed to retire and live out his days peacefully with his son.
- Tetricus II, caesar under his father.
- Vabalathus, 267-272. Emperor of the Palmyrene empire in Syria. Initially friendly with Aurelian, but then went to war with him. Captured and either died en route to Rome, or was allowed retire to sip margaritas with the Tetricii.
Fourth row:
- Aurelian 270-275. Top commander under Gallienus and Claudius II, then seized power from Quintillus. Succeeded in pushing back nearly every barbarian invasion, then reclaimed the Gallic and Palmyrene empires, but abandoned the province of Dacia permanently. Increased the size of the antoninianus, and set the fineness at 4.76%. Murdered when a secretary told a lie, and forged execution orders out of fear of punishment.
- Severina, 275. Wife of Aurelian, she ruled the empire as classical Rome's only empress for a few weeks. Forced to step down when the Senate nominated a successor.
- Tacitus, 275-276. Elderly senator, and the last person ever to be appointed emperor by the Senate. Died of old age after 10 months in office.
- (missing) Florian, 276. Brother of Tacitus, ruled for 88 days. Very scarce.
- Probus, 276-282. Governor of the East under Aurelian and Tacitus, declared emperor against and defeated Florian. Continued to repel invasions and attempted to repopulate the frontier lands. Murdered by disaffected troops.
- Carus 282-283. Former senator and praetorian prefect under Probus; proclaimed emperor when Probus was murdered. Led very successful campaigns and sacked the Sassanian capital of Ctesiphon. Died at age 61, reportedly when his tent was struck by lightning.
- Carinus, 283-285. Eldest son of Carus, and left in charge of the West. Said to have been a tyrant and a womanizer. Led some opposition against Diocletian, who was victorious and erased records of Carinus via Damnatio Memoriae.
- (missing) Magnia Urbica, wife of Carinus. Very rare.
- (missing) Nigrinian, son of Carinus. Exceptionally rare.
- Numerian, 283-284. Accompanied his father in the East, and assumed control of that portion on Carus' death. Said to be likable and well-read. Fell ill and was confined to a closed coach with his advisors being the only ones allowed to see him. The army forced their way into the coach and found a rotting corpse. His advisors were put to death and Diocletian declared emperor in competition with Carinus.
Fifth row:
- Diocletian, 284-305. Captain of the cavalry under Numerian, defeated Carinus after about a year of campaigning. Generally credited with bringing an end to the Crisis when he established his Tetrarchy system of organized co-rule between four emperors. Officially brought the old system of Roman currency to an end with a reformed system centered around the much more massive follis.
- Carausius 286-293. Renegade general of Diocletian who declared Britain as an independent Roman empire. An intellectual fellow who fancied that he would usher in a new golden age for Rome. Killed by his finance minister Allectus.
- Allectus 293-296. Killed Carausius and continued the sentiment of British independence as a new Rome. Defeated by Constantius I Chlorus, father of Constantine the Great.
Sixth row:
An assortment of "barbarous radiates". These are non-official copies of the antoninianus that are thought to have filled the role of small change when Aurelian reformed the Antoninianus in about 272. They range from decent, literate copies all the way down to comically childish, illiterate babble. Nearly all that have coherent legends show the name of Tetricus, but they can also be found of Victorinus, Claudius II, Gallienus, and Postumus.