The reported armies for both Theophilos' 837 expedition and Mu'tasim's retaliatory campaign are of unusual size. Some scholars, like Bury and Treadgold, accept the figures of Tabari and Michael the Syrian as more or less accurate,[9] but other modern researchers are sceptical of such numbers, as medieval field armies were rarely more than 10,000 men strong, and both Byzantine and Arab military treatises and accounts suggest that armies usually numbered around 4,000–5,000. Even during the phase of continuous Byzantine military expansion in the late 10th century, Byzantine military manuals mention armies of 25,000 as exceptionally large and fit to be led by the emperor in person. By way of comparison, the total nominal military forces available to Byzantium in the 9th century have been estimated at circa 100,000–120,000. For a detailed survey, see Whittow 1996, pp. 181–193 and Haldon 1999, pp. 101–103. Whittow, Mark (1996). The Making of Byzantium, 600–1025. Berkeley and Los Angeles, California: University of California Press. ISBN978-0-520-20496-6. Haldon, John (1999). Warfare, State and Society in the Byzantine World, 565–1204. London: UCL Press. ISBN1-85728-495-X.