The “vision” of Constantine, as recorded in Lactantius’ De mortibus persecutorum 44.5–6 and in Eusebius’ Ecclesiastical History 9.9.2–10, has been debated at length. The basic difficulty in these accounts lies in their presumed Christian bias. The inscription on the Arch of Constantine, however, provides a government-sanctioned record of the “vision” from a predominantly pagan viewpoint. The expression instinctu divinitatis on the arch has been linked to the phrase instinctu divino in Panegyrici Latini 12.11.4 (delivered in 313). It seems, however, that the proximate source is the phrase instinctu deorum from the account by Florus (Epitome 1.3.1–2) of the expulsion of the “tyrant” Tarquin the Proud. The ultimate source appears to be the concept of instinctu divino as explained in Cicero’s De divinatione [End Page 647] which became a “text” for foreknowing the will of the gods. The connotation of the phrase was preserved into late antiquity, not only by the continued study of Cicero but also through such authors as Livy, Seneca, the panegyrists, and Lactantius. Constantine demonstrated his knowledge of Cicero’s text in a speech given in 324. The senate’s appropriation of this term for the arch-inscription suggests that even pagans may have accepted some version of the “vision” of Constantine as early as 312–315.
IMP. CAES. FL. CONSTANTINO MAXIMO
P. F. AVGVSTO S. P. Q. R.
QUOD INSTINCTV DIVINITATIS MENTIS
MAGNITVDINE CVM EXERCITV SVO
TAM DE TYRANNO QVAM DE OMNI EIVS
FACTIONE VNO TEMPORE IVSTIS
REMPUBLICAM VLTVS EST ARMIS
ARCVM TRIVMPHIS INSIGNEM DICAVIT
LIBERATORI VRBIS FVNDATORI QVIETIS
To the emperor Caesar Flavius Constantinus Maximus, Pius Felix Augustus, the Roman Senate and the People have [lit., has] dedicated [this] arch, [as] the mark for triumphs because, by the inspiration of divinity [and] by the greatness of [his] mind, he with his army has avenged with just weapons the republic at one time as much from the tyrant as from all his party. To the liberator of the city. To the founder of quiet. 1
On 28 October 312 the army of Constantine defeated the army of Maxentius at the battle of the Milvian Bridge. By 315 the senate of Rome had erected a triumphal arch to commemorate the victory of the insurgent, Constantine, over his opponent. 2 The inscription was carefully worded in terms that would not only honor the victor but would also be in harmony with the religious and cultural beliefs of the pagan [End Page 648] senate. Furthermore, the very words on the arch, which was in effect a “billboard” for the victor, glorified the imperator in terms that were freighted with meaning for the populace of fourth-century Rome. 3
The prominence given to instinctu divinitatis as the cause of victory is noteworthy. The position of this phrase, which is placed immediately after the dedicatory phrases naming the emperor and the senate and the “people,” emphasizes the importance of this attribute. Because an expression like instinctu divinitatis (as well as magnitudine mentis) does not conform to the usual expressions of praise on triumphal arches, one is prompted to inquire further into the ideas that would have resonated in the minds of contemporary readers.4 A careful analysis of the contemporary implications of the term instinctu, as used in the arch inscription and other accounts, suggests that the story of Constantine’s “vision” (or “inspiration” by divinitas) was already current in Rome at a time close to the victory over the “tyrant.” [End Page 649]
The Significance of the Arch of Constantine
There are four key ancient witnesses for Constantine’s motivation and triumph in the years 312–15: the arch-inscription, the panegyric of 313, the account of Lactantius in 314 or 315, and the account of Eusebius in 313. Because the inscription on the Arch of Constantine was a government-sanctioned record of the outcome of the battle at a nearly contemporary date, it must be reflective of the mentalité of the governing classes in a way that no other record of the event is.
A preeminent authority on the prosopography of the later Roman Empire, A. H. M. Jones, observed: “the old senatorial...