Mohammed died in 632 as his followers swarmed on the Byzantine Empire. The Byzantine defeat at the battle of Yarmuk in 636 led to the loss of Syria, rapidly followed by Egypt and other North African possessions. Arabs besieged Constantinople in 674-678 and 717-718. The Byzantines' great rival, Sassanid Persia, was destroyed by the Muslims after the battle of al-Qadisiyya in 637. The broad sequence of events is well-understood, and obviously critical for the histories of the Byzantine, Sassanid and Arab Empires. With the lack of a recent work discussing these events from the Byzantine point of view, Kaegi's work is welcome. Donner's magisterial "Early Islamic Conquests" (Princeton, 1981) is almost entirely concerned with the Muslim point of view, while recent studies of seventh-century Byzantium (Stratos, Haldon) are more general. K. concentrates on the question of why the Byzantine empire failed to defeat the Arabs and avoids discussion of the conquest of Egypt and Sassanid Persia, stopping the story in the early 640s.
1) The sources for the seventh century are tantalizing. Potential sources could be divided into three groups, Byzantine, Arab and Sassanid. No Sassanid historical writing survives, while the Byzantine material is depressing. There is no great contemporary historian, no Theophylact or Procopius, while much of the material provided by later writers, by Theophanes or Michael the Syrian, actually comes from Arab sources (eg. 91-2), though K.'s explanation needs more depth (on these problems, Averil Cameron and L. Conrad, eds., "The Byzantine and Early Islamic Near East. vol 1: Problems in the Literary Sources" (Princeton, 1992)). But there are a few Byzantine sources from the seventh century, including a number of religious works from Syria-Palestine, which K. exploits well to show moods in the region (ch. 9 + appdx).
The core of our knowledge, however, remains the Arabic sources. These are plentiful and detailed, listing many of the leaders in the campaigns and providing dates down to the day for many events. But none of this material is contemporary and most of it appears to be written down in the late-eighth century or later. This in itself would not be worrying, except that the Arab sources can be divided into two different major traditions, both of which have different chronologies and events (here I follow Donner). In this context it is probably important that the Koran itself was not written down until the middle of the seventh century at the earliest, making it highly unlikely that there were contemporary sources for later writers like Ishaq and Washidi to work from. Indeed, Donner (128) warns that 'all of these chronological schemes are at heart later efforts to bring order to a mass of fragmentary accounts about the conquests in Syria, and though one such scheme may appear to be more plausible than another, all are essentially guesswork and none has any real claim to validity.' Nonetheless, K. conflates chronologies to produce a sequence of events. Whilst his sequence is plausible, it does not address or resolve all the problems with the source material. I do accept that this is an impossible task, but one has to be aware of the strength of the foundations one is building.
2) The Arab invasions came as a surprise to the Romans and Byzantines. They had faced no serious problems from their desert frontiers since the Palmyrene revolt at the end of the third century. The Palestinian frontier required regular patrolling and work against bandits, but garrisons, allied Arabs and a thin scatter of forts defended water sources and generally kept the peace. Three centuries of success is harshly dealt with: 'the wonder is that there had not been some major debacle earlier' (275)(c3, 10).
A brief period of Sassanid occupation of the Levant (c613-628) had been overturned by Heraclius and the area reoccupied by the Byzantines. When the first Arab probes began, the Byzantines had controlled the area for less than a decade, so were not well-settled. Nonetheless, K. is confident that they knew something about what was happening in the desert and Heraclius is blamed for a failure 'to make efficient defensive preparations against the Muslims' (76). K. limits his discussion to the Byzantines and unfortunately there is no discussion of the Arabs, who they were, and why they were attacking the Empire. The defeat at the Yarmuk 'exposed the Byzantines' fallacious assumption that they were dealing with mere beduin, rather than the co- ordinated army of a new state' (137), but some discussion of how justified the Byzantines were in this assumption would be in order. Were they complacent, or just ignorant of what was happening at Medina?
The initial Arab raiders were able to defeat the Byzantines in several small clashes and could now be seen as more than a passing menace. Their armies increased in size. Heraclius' initial response was probably 'where on earth did 20,000+ Arabs come from?' The scale of the threat had changed, and it was recognized, with Heraclius' despatch of the field army which was defeated at the Yarmuk (c6).
3) Much turns on the battle at the Yarmuk, but analysis is difficult. An idea of the problems are given by Donner's estimates for the Byzantine army, c100,000 (Donner 132), as opposed to K.'s, 15-20,000 (131). The battle opened well for the Byzantines, who pushed the Arabs back to their camp. This was the expected result. Then something went wrong, the Arabs broke part of the Byzantine line and forced them into a wadi. Later, the Byzantines tried to break out, but were massacred. This is clearly not one but two battles and one of the Arab traditions (Tabari) suggests a month-long interval between the first clashes and the breakout from the wadi. Almost every battle fought before 1900 was over in a day, so what is happening here? The sources do not allow a simple answer, but might suggest that the initial Byzantine defeat was not the rout it is often said to be.
4) Once the battle was lost, the Byzantines lost control over Syria and were not able to launch an attempt to recapture the region (c7). The Arabs were able to pick off the various Byzantine towns in the area, with coastal cities falling later than those inland. K. complains that Byzantine strategy was flawed and that they should not have relied on fortified towns (c3). Instead, he continually recommends that the Byzantines fight on a defensive line in Syria. He decries what he describes as defense-in-depth, preferring instead 'a frontal/forward linear defense along some fixed barrier' (60), surely an anachronistic concept. Even without linear defense, his criticism is harsh. Few towns fell before the battle of the Yarmuk, while this strategy had been used successfully throughout the empire since the third century. Furthermore, the loss of towns was the result of losing the field battle in the first place, and what precedent was there for that?
If anything, the failure was the Byzantine inability to produce a second field army. The Byzantine Empire was strained in finance and manpower while the eastern provinces were still readjusting to Roman rule. The Arabs arrived at a bad time. Other problems did not cease after the Yarmuk. Rebellions in Africa and a succession crisis all detracted from the Byzantine ability to raise a new field army to reconquer Syria (261-2).
K. complains that there is no evidence of new Byzantine strategy or tactics following the Arab conquests (206). Was this because they were inept, or because there was no need to adapt? Given our lack of knowledge as to what happened on the battlefield, there is no reason to suppose that the Byzantines failed at a tactical or operational level. From the 640s onward, the Arabs were unable to invade Asia Minor (as opposed to raiding), so there may not have been too much wrong with the Byzantine strategic system, a point made, but not fully developed (243). The Arabs then changed to a marine strategy, resulting in the sieges of Constantinople between 674 and 678, perhaps suggesting this was easier than a direct land assault.
Here, the lack of mention of Arab organization and military methods is felt, while a brief description of the Byzantine army would also have been in order. The Byzantine fleet is remarkable by its absence in these wars, a point K. raises only briefly (277). Since the fleet was instrumental in saving Constantinople from sieges in 626 and 678, its absence is a historical problem.
5) In his conclusion, K. states that 'the situation of the Byzantine Empire in the middle of the 640s had not been foreseeable in 628 or 629' (286). The blame is placed on four new elements, Islam, numbers of Arabs, Byzantine fiscal problems and the new direction of the threat (274-5), none of which are the focus of K.'s work. Indeed, this conclusion comes as a surprise given the stress on poor Byzantine strategy throughout the work.
Although much of this review has been critical, the poor source material makes it necessary to be very clear about where one stands. K deserves congratulations for making much of it accessible. When combined with Donner and a more general survey of seventh-century Byzantium, we are able to gain a new perspective on the conquests, one which will surely spur further work. The issues, however, are too big for a single book, and K. was probably wise not to try.