Thomas Aquinas’s De regno is the saint’s contribution to the “mirror of princes” genre. Written for a king of Cyprus and left unfinished, it is often considered Aquinas’s contribution to political theory. Scholarly attention has focused on its date, as a difference of a few years would make a significant difference in the king of Cyprus for whom it was written and the broader political circumstances of its writing. However, there is an interesting biographical issue posed by the De regno. In the sections believed to be written by Thomas, there is no mention of Frederick II, the Holy Roman Emperor. While Aquinas’s project in the De regno was by no means a conspectus of contemporary politics or recent history, the silence about Frederick II is interesting because the case of the Hohenstaufen emperor has direct bearing on a question Aquinas treats at length—the problem of tyranny.

Aquinas’s recent biographer, Jean-Pierre Torrell, O.P., implies that the primary controversy over the De regno regards its date (Saint Thomas Aquinas: Vol. 1: The Person and His Work, pp. 169–70.) It is not an insignificant problem. The precise date of the De regno would necessarily change the king of Cyprus to whom it was addressed. A date of 1265 or 1267—favored, per Torrell, by Echard, Mandonnet, and Eschmann—means that Thomas was writing to Hugh II of Cyprus. Torrell suggests that the 1265-67 dating is unacceptable because the De regno relies on the commentary on the Ethics, which is clearly later.  A slightly later date of 1271, however, means that Thomas was writing to Hugh III of Cyprus. (Hugh II died in 1267.) The problem with that is that Hugh III was a rival claimant to Charles of Anjou for the kingdom of Jerusalem. Torrell may overstate the rivalry, however, since Hugh III was accepted by the legalistic barons of Outremer as king of Jerusalem in 1269. Charles’s purchase of the rejected claim of Mary of Antioch was not concluded until 1276.

All of this is interesting, to be sure. But the De regno is deeply concerned with the problem of tyranny. This no doubt is because the work is a speculum principis, and as a fundamentally practical treatise it is aimed toward a major practical problem of princes: how to avoid being a tyrant. However, the book makes no reference to Frederick II. It cannot be said that Frederick would have been an obscure figure, either to Thomas or to a Lusignan king of Cyprus (or Jerusalem). To understand why this is interesting, a brief tour of Thomas Aquinas’s biography—with special reference to Frederick II—is necessary.

The canned biography of Thomas Aquinas that everyone has by heart is that he was born to the powerful Aquino family. His father, Landulf, was a knight in the service of King Roger of Sicily and then one of Frederick’s officials. The family then became deeply embroiled in the battle between Frederick II and Pope Innocent IV, as most noble families in Italy did. Landulf’s oldest son, Aimo, went to the Holy Land in Frederick’s service, was captured by a supporter of Hugh of Cyprus, and ransomed by the pope’s party. Aimo stayed firmly with the pope thereafter. Landulf’s second son, Rinaldo, was a supporter of Frederick until Innocent deposed him in 1245. Frederick executed Rinaldo shortly thereafter, in 1246. According to Torrell, who summarizes this history and provides references to various primary sources, the Aquino family viewed Rinaldo as a martyr for the Church.

As everyone knows, Aquinas’s family sent him to the influential Benedictine monastery of Monte Cassino. Landulf offered him as an oblate, and it is usual to speculate that Landulf imagined the young Thomas eventually becoming abbot of the famous, wealthy monastery. At some point between 1230 and 1231, Aquinas entered Monte Cassino and received his earliest education there. However, in 1236, as the peace between Frederick and the papacy began to break down, Landulf, on the advice of the abbot, took Thomas from Cassino and sent him to Naples to continue his studies. We know that Frederick founded the University of Naples in 1224 as a rival to the University of Bologna and he required his Sicilian subjects to study there. We also know that it was at Naples where Thomas first encountered Dominican friars, who had been present at the university since 1231.

Frederick was, directly or indirectly, involved closely with the Aquino family, and provided the conditions for Thomas’s early education. However, Frederick may have been even more closely involved with Thomas’s early life. The famous incident of Thomas’s entry into the Dominicans provides, in Torrell’s telling, some additional clues as to Frederick’s involvement with the Aquino family and with Thomas in particular.

All the biographies mention the Aquino family’s steadfast resistance to Thomas’s entry into the Dominicans. There were no doubt several factors behind this. No doubt first and foremost among them was the family’s plan that Thomas should become abbot at Monte Cassino. Another factor may have been Frederick’s hostility to mendicant orders. In any event, after Thomas took the Dominican habit in the spring of 1244, informed his family, and set out for the general chapter in the company of John the Teuton, then the master general of the Order of Preachers. His family reacted badly to the news. His mother went to Naples and Rome to try to dissuade Thomas; she then informed his brothers, who were with Frederick II’s army, who made plans to lay hands on Thomas by force.

Torrell provides an extremely interesting detail about this episode. Two men in the party that arrested Thomas are named: his brother Rinaldo and Piero della Vigna. Della Vigna’s presence is extremely interesting. In the spring of 1244, Della Vigna would have been one of the most important men in Frederick’s empire. Indeed, after Frederick himself, Della Vigna may have been the most important man in the Empire, as Frederick’s chancellor, secretary, mouthpiece, and theorist. Ernst Kantorowicz’s brilliant biography, Kaiser Friedrich der Zweite, presents Della Vigna as an indispensable figure in Frederick’s court and one of the cultural luminaries of Italy and the Empire. Torrell observes drily that Della Vigna’s presence in the party that arrested young Thomas Aquinas meant that Frederick likely personally approved the arrest. This much is surely true.

So far from being merely a distant ruler, Frederick was almost an intimate of the Aquino family. Not only was Frederick a patron and ally (and later enemy) of Thomas’s father and brothers, but he also was undoubtedly informed of the operation to prevent Thomas’s entry into the Dominicans, sending his important deputy (almost his alter ego, in Kantorowicz’s telling), Piero della Vigna, as part of the party that arrested Thomas. This supposes intimate knowledge on Frederick’s part about Thomas’s entry into the Dominicans and his family’s objections. After Frederick’s break with Innocent IV—more on that in a moment—Thomas’s brother, Aimo, joined the pope’s party. Frederick ordered the execution of Thomas’s other brother, Rinaldo.

About a year after the high drama of Thomas’s arrest and imprisonment, at the Council of Lyons, Pope Innocent IV issued Ad apostolicae dignitatis apicem, which excommunicated Frederick and deposed him as king of Sicily and Roman emperor. The story of the break between Frederick and Innocent IV would be too long to recount in detail, since it marked the culmination of over twenty years of tension with the Church, going back to Innocent III and Gregory IX. Innocent alleged that Frederick, despite his oaths of fidelity to the popes, made war against the Church and was suspect of heresy. In Kaiser Friedrich der Zweite, Ernst Kantorowicz (fairly convincingly) argues that Frederick’s combat against the Lombard League and his desire to unify territorially the Empire with Sicily—which would have left the Papal States surrounded by Hohenstaufen possessions—was at the root of the conflict between first Gregory IX and then Innocent IV.

However, one of Innocent’s specific charges ought to be examined in particular. After rehearsing Frederick’s alleged perjuries and broken pacts with the Church and his putative heresy, Innocent turns to Frederick’s putative maladministration of the kingdom of Sicily.

Praeter haec regnum Siciliae, quod est speciale patrimonium beati Petri et idem princeps ab apostolica sede tenebat in feudum, iam ad tantam in clericis et laicis exinanitionem servitutem que redegit, quod eis paene penitus nihil habentibus et omnibus exinde fere probis eiectis, illos qui remanserunt ibidem sub servili quasi conditione vivere ac Romanam ecclesiam, cuius principaliter sunt homines et vassalli, offendere multipliciter et hostiliter impugnare compellit.

(Oddly, the Vatican makes the Latin original available on its website.) In translation, this charge reads:

Besides this the kingdom of Sicily, which is the special patrimony of blessed Peter and which Frederick held as a fief from the apostolic see, he has reduced to such a state of utter desolation and servitude, with regard to both clergy and laity, that these have practically nothing at all; and as nearly all upright people have been driven out, he has forced those who remain to live in an almost servile condition and to wrong in many ways and attack the Roman church, of which in the first place they are subjects and vassals. He could also be rightly blamed because for more than nine years he has failed to pay the annual pension of a thousand gold pieces, which he is bound to pay to the Roman church for this kingdom.

While not phrased in terms of tyranny and the common good, it is clear that Frederick’s civil maladministration in Sicily comes very near to tyranny in Innocent’s eyes. Running throughout the bull is the charge that Frederick has broken the peace between the Empire and the Church; this charge suggests that Frederick has thrown Sicily into disorder and reduced everyone to poverty, desolation, and servitude. He has also led them into moral turpitude.

This, then, is the interesting biographical problem: writing not quite thirty years after Innocent deposed Frederick, at least in part for Frederick’s alleged tyranny, Aquinas does not mention Frederick at all in his speculum principis, which is concerned preeminently with keeping a prince from falling into tyranny. Given Innocent IV’s charges against Frederick, one might reasonably assume that Frederick would be a clear example of a modern tyrant in Thomas’s account. Frederick, according to Innocent, abandoned the common good of his Sicilian subjects to draft them in his war against the Church. More than this, Frederick’s conflict with Innocent IV embroiled the Aquino family, ultimately to the price of Rinaldo d’Aquino’s life. Thomas, therefore, would have a personal motivation to discuss Frederick as a tyrant.

That he does not is, of course, extremely interesting. Perhaps his silence can be explained in terms of his project in the De regno. Observe—we are sure you no doubt have observed, dear reader—that Aquinas cites classical authors such as Aristotle, Cicero, Vegetius, and Vitruvius. He also cites scripture and Augustine at some length. One could argue that Aquinas avoids contemporary or near-contemporary politics in order to make his case based solely on scripture and classical authors—including for the moment Augustine in the list of classical authors. After all, the case of Frederick II and his children and grandchildren would have been very much on the mind of Hugh II/III of Cyprus. The Lusignan kings of Cyprus had benefitted from the fall of the Hohenstaufens, particularly with respect to their claims to Jerusalem. One might argue that it was wholly unnecessary for Thomas to rehearse the case of Frederick II in the De regno. (One could also argue that the De regno is incomplete, but there’s no fun in that argument.)

However, that explanation is perhaps not wholly satisfactory, especially given Thomas’s treatment of the options of a people laboring under the yoke of a tyrant. This is not the place to get into that question in depth, but it is worth noting that Innocent IV purported to depose Frederick II from both the Empire and Sicily. The case of Sicily is relatively straightforward, since it was a papal fief. However, deposing the Roman Emperor was another matter. Innocent’s decision caused significant disruptions in the political order of Europe, though Frederick’s deposition was never meaningfully effected. The question of papal involvement in the deposition of a tyrant was therefore a major question in relatively recent history—and Thomas is silent about it.