In order to calculate the relative value of the amounts of grain mentioned in the various sources as provided by the thematic authorities for various expeditions, as well as the numbers of animals required to transport a specific quantity of supplies for men and animals over a specific period of time, the value of the measures which are used must first be established, and this is still to a degree problematic, in spite of the work of several specialist scholars. Such calculations depend on a range of variables which have aroused a great deal of disagreement. The measure used in the majority of texts dealing with grain from the middle Byzantine period is the modios, but since there were several different modioi, and since the relationship between the various modioi and other measures, such as the litra (the Roman pound), on the one hand and, on the other, late ancient values for weight and volume such as the artaba remain unclear, it is not possible simply to read off the values from the texts in question.
Most of the information on the relationship between the artaba and the modios for the late Roman period comes from Egyptian documents, and although there are some difficulties (because of the variety of equivalences given in different localities), an equivalence of 4.5 basic (or “Roman”) modioi or 3.3 modioi xystoi to the artaba can be derived from fiscal documents of the fifth and sixth centuries; nevertheless there are several other equivalences, depending on which of the various modioi are meant.1 The issue is complicated by the fact that the modios is a measure of volume or capacity, and that in consequence it is difficult to extrapolate a weight in order to calculate the results of any conversion from grain to flour and thence through the baking process to bread. Equivalences between volume and weight must therefore remain averages, the more so since different types of grains weighed differently and were of different density, so that a modios of barley is by no means the same quantity, by weight or by product, as a modios of wheat.2 Matters are further complicated by other factors, in particular the variable value of the Roman pound (calculated at 327.45 g in the late Roman period), which in the middle Byzantine period had fluctuated to a mean of as little as 320 g in the ninth to the tenth centuries, thus further reducing the weight-value of the modioi in question.3 The annonikos modios has been calculated at 26.6 Roman pounds (at 320 g to the pound, i. e. 18.75 lb avoirdupois/8.7 kg).4 This was probably the modios used to calculate the military synone, a conclusion based on calculations using middle Byzantine figures for pack-animal loads.
The approximate maximum weight a horse or mule can transport over reasonably long distances is about 250 lb (114 kg),5 and a little more over short stretches, although the optimum has generally been set at about 200 lb in modern and immediately pre-modern pack-trains.6 In the late third-century Edict of Diocletian (14.11) a load of 200 Roman pounds (65.49 kg/144 lb) is prescribed; a sixth-century source gives mules a total burden of 156—66 Roman pounds (110—16 lb/50—3 kg).7 Similar limits are established by the imperial legislation on the public post.8 A mid-tenth-century Byzantine text gives somewhat higher levels, as we have noted in Chapter 5 above: three categories of load are specified: (a) saddle-horses carrying a man (presumably not armoured and carrying military panoply) and their own barley were loaded with four modioi each—106 Roman pounds=75 lb (34 kg); (b) unridden saddle-horses carried eight modioi—212 Roman pounds=150 lb (68 kg); and (c) pack-animals loaded with barley carried ten modioi—265 Roman pounds= 187 lb (85 kg).9 Thus the maximum permitted load for an animal in the imperial baggage train in the ninth and tenth centuries was set at 10 modioi without the pack-saddle (sagma) and harness which, according to the legislation of the fourth-sixth centuries, weighed approx. 50—60 Roman pounds (35—42 lb/16—19 kg, equivalent to 51—62 Byzantine pounds).10 Using the larger thalassios modios of 40 Byzantine pounds as a basis for calculations, the result would be an impossibly heavy load of 450 Roman pounds, or 144 kg/319 lb avoirdupois. Using the smaller annonikos modios of 26.6 Byzantine pounds, the load would weigh some 266 Byzantine pounds, and with the pack saddle, a total of 316 pounds, i. e. c. 101kg/223 lb. Given the various weight limits decreed in the different late Roman and Byzantine sources referred to, these results strongly suggest the annonikos modios as the basis for calculation of middle Byzantine military supplies. The figures tally also with those generated by scholars who have studied late Roman or Hellenistic transportation, especially the loads carried by horses and mules. No single figure for “average” loads has been produced, however, for several reasons. First, the exact meaning of, and the relationship between, the weights and measures used by ancient and medieval writers are still debated; second, the size of the animals plays an important role—the carrying capacity of a mule or horse is in direct relationship to the weight and stature of the animal—the smaller the animal, the less they can carry and the more of them that may be required. Lastly, local variations in climate, ground and so on also played an important role, and these factors are hardly ever mentioned in connection with the use of animals in warfare.11 For the purposes of the present discussion, I have used the tenth-century Byzantine figures, modified where appropriate (or where relevant information is lacking) by more recent analyses of the capacities and needs of these animals in military contexts.
In the estimates below, therefore, I will take the average weight for a horseman to be 154 lb (70 kg) and, based on Roman information, the weight of his accoutrements as a further 6 kg for clothing, 14 kg for a mail shirt, 1.4 kg for a helmet, 5.5 kg for a light shield, 2 kg for a spear, 1 kg for a light sword or sabre and 12 kg for a military saddle and harness.12 The total thus amounts to some 112 kg (approx. 246 lb). A horseman thus equipped would not be able to carry much extra weight without damaging his mount—a maximum of 3—4 kg (between 6 and 9 lb), sufficient for three-four days’ supplies for himself, or about one day’s worth for both himself and his mount: note that both the late sixth-century Strategikon and the tenth-century treatise on Skirmishing recommend that cavalry soldiers carry three to four days’ supply with them in their saddle bags.13
As far as concerns the pack-animals and unridden spare mounts, I will take for the latter the maximum load specified in the tenth-century military treatise on imperial expeditions, that is 8 modioi—212 Roman pounds or 150 lb (68 kg)—which, together with a military saddle of about 10—12 kg makes a total of some 80 kg (or with the heavier framed pack-saddle, or sagma, which weighed between 50 and 60 Roman pounds, 35—42 lb/16—19 kg, a total of about 84—7 kg).14 I will also assume that, under certain conditions, the spare mounts accompanying cavalry units will have been used to carry provisions and supplies, but that the lower figure given in the treatise reflects the practice of keeping their loads light so that they do not lose spirit or become worn out.15
For the regular mules and pack-horses, the same treatise specifies a load of 10 modioi, i. e. 265 Roman pounds=187 lb (85 kg) which, with pack-saddle and harness, would thus amount to some 100—2 kg (227 lb). This is not the maximum, and since the average capacity has been estimated from other historical examples to have been slightly higher, I will take the standard figure of 250 lb (113.6 kg) as the maximum weight that could be borne, including saddle and harness, so that the average load carried would amount to approximately 96 kg (211 lb) (making 112—115 kg with the pack-saddle).
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