The House of Constantine at War: Persia, Strasbourg, and the Road to Ctesiphon

The Brothers' Wars and the Persian Front337–353

The dynasty opened with the murder of most of itself — the summer massacre of 337, in which the army at Constantinople killed two half-brothers of the dead emperor and seven cousins, sparing two boys, and the tradition's assignment of responsibility to Constantius II was contested then and is unresolvable now — and then divided the world three ways among the sons: Constantine II the far West, Constans Italy-Africa-Illyricum, Constantius the East, an arrangement that lasted until 340, when the eldest invaded his brother and died in an ambush at Aquileia, and 350, when Constans was hunted down by the agents of the usurper Magnentius, a Frankish-descended field officer proclaimed in Gaul.

The decisive fraternal war was therefore Constantius against Magnentius, and its decision at Mursa in Pannonia on 28 September 351 was the fourth century's costliest day: the epitomators' figures — twenty-four thousand of Magnentius's fifty-four thousand, thirty thousand of Constantius's eighty — are tradition's arithmetic, but the tradition's verdict is unanimous and the Editor endorses its substance: a Roman bloodletting, cavalry-decided (the eastern clibanarii and mounted archers breaking the western legions against the Drava), from which the western field army never fully recovered, its veterans spent three years before the Rhine's defense would need them; Magnentius fell back through Italy and Gaul to die on his own sword at Lyon in 353.

Meanwhile the East fought the war Constantine had left in the files. Shapur II — crowned before birth, by the tradition, and reigning seventy years — reopened the Mesopotamian war in 337/8, and for twenty-five years it ran as a siege-war on the fortress-line the Peace of Nisibis had drawn: Nisibis itself thrice besieged (338, 346, 350) and thrice held — the third siege the epic of the age, Shapur damming the Mygdonius to float siege-craft and collapse the wall by flood, the breach assaulted by elephants and armored cavalry across the mud and the city living because the garrison walled the gap in a night — Singara the site of the one great field battle (344 or 348), a Roman day lost by night when the pursuing army stormed the Persian camp and was destroyed in it by moonlight and archery; Amida's nine-week agony belongs to the next section because Ammianus was inside it. The Editor marks the front's character for the volume's argument: this was positional, engineering-heavy, attritional warfare between peer states — the limitanei and the fortress-architecture of Chapter 1 doing exactly what they were built for — and it held.

Julian: Strasbourg and the Persian Catastrophe355–363

The reign's last decade belongs to the cousin the massacre spared. Julian — twenty-three, a student of philosophy with no military hour behind him — was created Caesar in 355 and sent to a Gaul wrecked by the civil war's stripping of the Rhine: Cologne fallen, forty-five towns sacked, the Alamanni settled on the left bank.

What followed made him, and the compendium has the luxury, unique in this volume, of narrating it through a great historian who served in the theater: Ammianus's books carry the campaigns of 356–358 — Cologne recovered, the Rhine line re-bridged, the supply-fleet from Britain reinstituted — and their crown at STRASBOURG (Argentoratum), August 357: Julian with perhaps thirteen thousand against the confederated Alamanni under Chnodomar, thirty-five thousand by the account; the Roman cavalry broken at the outset — the mailed cataphracti bolting through their own infantry, rallied by the Caesar in person with the shame-speech Ammianus stages; the infantry battle the account's core, the Alamannic wedge splitting the first line, the primani legion holding the second like a wall; the collapse and the drowning pursuit to the Rhine, six thousand Alamanni dead on the field against two hundred and forty-three Romans by the historian's count — printed as the historian's — and King Chnodomar taken.

Strasbourg restored the Rhine for a generation, and the sequel restored the pattern of the age: the army of Gaul, ordered east in 360 to feed Constantius's Persian war, mutinied at Paris and raised Julian on a shield — the acclamation German in form, the historian notes, as the army now half was — and civil war was prevented only by Constantius's death in Cilicia in November 361, leaving Julian sole Augustus: the last pagan, the emperor-philosopher, and the author of this compendium's final author-is-subject corpus, whose reign of twenty months was consumed by the religious restoration and the preparation of the war that ended it.

The Persian expedition of 363 was the East's largest offensive since Trajan: sixty-five thousand men, a fleet of over a thousand river-craft, a feint through Armenia under Procopius, the main army down the Euphrates — Ammianus marching in it — through the canal into the Tigris, the fortress-towns stormed or bypassed in sequence, a pitched victory won under the walls of CTESIPHON in late May; and then the campaign's self-destruction, in the sequence the sources dispute and the Editor prints as the participant reports it: the council's judgment that the capital could not be besieged, the decision to march inland to join Procopius, and the burning of the fleet — a thousand ships, the army's bridge and granary, fired at the emperor's order to free their crews for the column and deny them to Persia, the act every subsequent tradition treated as the death-warrant; then the scorched-earth withdrawal up the Tigris in the June heat, the Persian shadow-army's daily stings, and on 26 June, in a rearguard action near Samarra (Maranga), the emperor — riding unarmored into the melee — took a spear through the ribs and died at midnight in his tent, thirty-one years old, discoursing (the deathbed scene is Ammianus's, who says he was there or nearly) on the soul.

The army, starving and boxed, elected the guards-officer Jovian, and the price of extraction was the Peace of 363: the five trans-Tigris satrapies of 299 returned, Singara and the fortresses ceded, and NISIBIS — thrice-defended, never taken — handed to Persia intact, its Roman population marched out; Ammianus, who watched the evacuation, made it the Res Gestae's bitterest page, the crowds at the gates, the man carrying his household gods, the city that had held the East given away by treaty; and the Editor closes the chapter on his verdict and its audit: the historian blamed the shameful peace; the arithmetic blamed the burned fleet; and the frontier the treaty drew — Nisibis Persian, the line withdrawn — proved, in the volume's longest irony, durable: the East's next great war with Persia was a hundred and forty years away.