Editor's note: this is the third and final part of a feature about collecting coins of the Twelve Caesars that originally appears in full in the April Monthly issue of Coin World:

Early in the second century A.D., Gaius Suetonius Tranquillus authored a set of 12 biographies, the stories of the dictator Julius Caesar and the first 11 emperors of the Roman Empire, covering history from 49 B.C. to 96 A.D. These dozen rulers have become a popular focus for building a set of ancient coins — a Twelve Caesars set. The first two parts have covered approaches to building such a set, and we take up here with the fourth caesar, the mad Caligula:

The fourth emperor in the Twelve Caesars series was the madman Gaius (A.D. 37 to 41), better known to history as Caligula.

The reign of this ruler can present quite a challenge, as many of the coin types of his reign show, not the emperor, but his family. Among the few types that do bear his portrait, all the gold and silver issues are very rare.

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In gold or silver, Caligula is one of the most elusive on the list. Accept a bronze coin, and the task of filling his slot becomes much easier (but not necessarily more affordable if a portrait con is required). 

The only easily available portrait coin for this emperor enjoys tremendous demand, from collectors building the Twelve Caesars set and from those who are working on an Imperial portrait series.

Coinage of the next man, Claudius, is more extensive than that of his two predecessors, but a collector seeking to build a set of the Twelve Caesars in gold or silver will find Claudius a real challenge.

In base metal, several types appear in the marketplace with nearly equal frequency. All of them are asses, the copper coins of about half-dollar size that constituted one-sixteenth of a denarius. 

Sestertii and dupondii are also available but are scarcer than asses. If having the emperor’s portrait is not vital, a quadrans (plural: quadrantes), a tiny copper coin equal to one fourth of an as, or 1/64 of a denarius, can represent his reign.

The “Greek Imperial” coinage (local coinages struck in Greek-speaking parts of the Empire) is more extensive during this reign, making it somewhat easier and less expensive to obtain the emperor’s portrait if you don’t mind a coin with Greek legends instead of Latin ones. 

Last in the Julio-Claudian Dynasty was the infamous Nero (A.D. 54 to 68).

Most of Nero’s early coinage was struck in gold or silver, and many issues can be dated to specific years. Gold aureii were struck throughout Nero’s reign, with dated issues for every year except the last, A.D. 67 to 68. Consequently, relatively speaking, Nero is one of the easier emperors to obtain in gold.

Little base metal coinage was needed under Nero, so the mint merely counterstamped coins of Claudius (and occasionally those of his predecessors) for circulation. 

Nero’s coinage also includes an extensive issue of Greek Imperials, and collectors have no difficulty in obtaining an example.

Galba succeeded Nero in July of A.D. 68 and was assassinated after a reign of less than a year. The ensuing civil war produced two more key coins in the set, issued by the short-lived emperors Otho and Vitellius.

Considering the brevity of his reign, the number of coinage types of Galba is extensive, even not counting the many Greek Imperial issues. However, the coins are overall rare given the demand from those building Twelve Caesars sets and those working on a complete Roman portrait gallery. 

Gold coins of Galba are beyond the means of most collectors, and the silver denarii are expensive, so most collectors represent Galba with a base metal coin. 

M. Salvius Otho, the eighth ruler in the Twelve Caesars group, ensured that he followed Galba by having him assassinated on Jan. 15, 69. Otho did not enjoy his reign for long, though: on April 15, his armies were soundly defeated by Vitellius, and he committed suicide April 17.

Otho’s brief reign produced a very limited amount of coinage, and his issues are often regarded as the key coins of the Twelve Caesars set. His silver denarii are the third most difficult issue to acquire for the set, according to Phillips. Caligula and Claudius, whose other coinage is far more common than that of Otho, did not issue many denarii, so their coins in that denomination are rarer and more expensive.

Collectors on a budget should consider the Greek Imperial issues, base silver tetradrachms from Alexandria in Egypt, or bronze issues from cities in the Greek world.

Vitellius assumed power following Otho’s April suicide but was murdered in December 69, by the invading armies of Vespasian. 

Coins of Vitellius are among the scarcest in the Twelve Caesars series. Only Otho’s total coinage output was smaller. 

Because Vitellius struck a sizable quantity of denarii, though, his portrait on coins of that denomination is more available than portraits of Julius Caesar, Claudius, Caligula or Otho. He is the second scarcest of the Twelve Caesars overall, but only the fifth scarcest if your set is devoted to denarii.

Vespasian and his two sons, Titus and Domitian, constitute the Flavian Dynasty, which ruled Rome for 27 years, from 69 through 96. They are the last three emperors among the Twelve Caesars, but they are often the first three whose coins are acquired by numismatists. 

Coins with the portrait of Titus are somewhat scarcer than those of his father or brother, but not rare. Most of his coins are readily available and affordable, with the Judea Capta designs celebrating Vespasian’s success in beating back the First Revolt of the Jews (A.D. 67) a popular type.

Domitian’s reign marks the conclusion of the Twelve Caesars series, and his coins are among the least expensive in the set. His reign was the longest since that of Tiberius. 

The specialist in silver coinage will find denarii of Domitian plentiful and inexpensive compared to all the other reigns in the Twelve Caesars set except Vespasian’s.

Building a set of Twelve Caesars coins is an exercise in education, patience and perseverance. In time, it can be a rewarding pursuit blending the hobby and history.