Heather begins by describing the political maneuvering that, complemented by able generalship, secured Constantius' ascent to power. The goal of such high imperial politics was to eliminate rivals, but this, crucially, left the empire without a clear line of succession when Contantius died unexpectedly in 421 (given that his son was too young to rule). Twelve years of conpiracy and war ensued, from which the general Aetius emerged as the ruler (not as the emperor, but as more or less a regent for Theodosius, Constantius' son with Galla Placidia). Although the succession struggle was fairly normal by imperial standards, the situation was not: there were unsubdued barbarians in the empire who had a more or less free run while the rivals battled for control of the Western empire.
During this time, the Vandals and Alans crossed the Mediterranean to Africa and assaulted the rich Roman provinces near Carthage. The sources on the barbarian invaders thin out during the struggle to succeed Constantius, so all the details of why and how they got there are somewhat a matter of educated guesswork. Heather fills in a plausible story: seeing that Africa was relatively safe from Roman counterattack, the Vandals made the short passage to the far western provinces of Roman Africa, and then made a beeline for Carthage. The badly outnumbered and outclassed Roman forces in Africa were powerless to stop them.
At this point, Heather takes an excursus into a description of the importance of Roman North Africa, drawing on a range of sources. The remains of the port facilities of Carthage and Ostia bespeak the volume of shipping between North Africa and Rome. The ruins of the city of Carthage and provincial centers throughout its hinterland show how much the region profited from it. The trade was above all in staples like wheat and olive oil, but archaeology shows a variety of other goods, including wine and pottery, were also exported around the empire. Documentary evidence shows that Rome gave easy leases on public lands in North Africa, thus partially accounting for the size and profitability of agriculture there. The profitability of a larger range of cheap exports depended on low-cost transport, which Heather deduces was a result of the documented combination of compulsion and subsidy for the shipping profession.
Returning to Aetius, Heather lists the profusion of challenges facing the new Western leader -- besides the Vandals in Africa, the Suevi in Spain, the Visigoths and rebel local elements in Gaul, and various Germanic tribes along the frontier were all threatening the integrity of the empire -- and describes his response to them. Heather notes that the source material for the era is mostly bare chronicles, but for the European campaigns this is supplemented by a surviving palimpsest of parts of two panegyrics by Aetius' subordinate Merobaudes. From these sources, we know that Aetius secured two key alliances to deal with his challenges during the 430s. He got Constantinople to send an army to Carthage that compelled the Vandals to come to a deal for a peripheral slice of North Africa. He used an alliance with the Huns to subdue the rebels and contain the Visigoths in Gaul (Heather argues that he bought off the Huns with a slice of Pannonia to gain their help.) Finally, he was able to pressure the Suevi in Spain to come to an accommodation.
In 439, the Vandals under Geiseric took advantage of the opening provided by Aetius' preoccupation elsewhere to attack and capture Carthage and the key provinces of Proconsularis and Byzacena. A joint expedition with the Eastern Empire to reconquer the lost territories was called off in 441, and costly peace was made with the Vandals instead. Between the complete loss of revenue from the territory lost to the Vandals and greatly reduced take from what remained in Roman hands, a huge hole was opened in the Roman budget. Literary evidence reveals that this gap could not be filled even by eliminating all the perks granted to the privileged landowning class, and Heather infers that the army must have been drastically cut back as a result. Heather argues that there must have been a compelling reason to accept such a serious blow, and deduces from the sources that the reason was a new Hunnic threat that required the attention of the Empire in both East and West.
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