In book II, dealing with dialectic and rhetoric, Isidore is heavily indebted to translations from the Greek by Boethius, and in book III, he is similarly in debt to Cassiodorus, who provided the gist of Isidore's treatment of arithmetic. Caelius Aurelianus contributes generously to the part of book IV dealing with medicine. Isidore's view of Roman law in book V is viewed through the lens of the Visigothic compendiary called the "Breviary of Alaric", which was based on the Code of Theodosius, which Isidore never saw. Through Isidore's condensed paraphrase a third-hand memory of Roman law passed to the Early Middle Ages. Lactantius is the author most extensively quoted in book XI, concerning man. Books XII, XIII and XIV are largely based on Pliny the Elder's "Natural History" and Solinus, whereas the lost "Prata" of Suetonius, which can be partly pieced together from what is quoted in "Etymologiae", seems to have inspired the general plan of the work, as well as many of its details.