The historical turn in the social sciences has been neglected by historians. This has caused social scientists to use much data which has not been curated by experts focused on the relevant time periods and geographic locations. A recent article by Oka et al. investigating the important question of historical trends in violence is a good example. A detailed survey of Oka et al.’s Persian, Greek and Roman population, army size and casualty data reveals several problems. The uncertainty in ancient data, especially casualty figures, has been underappreciated by Oka et al. In population and army size data, some speculative and dependent data points have been treated as independent. There are also inconsistencies in the data and some inflated figures. The situation is worse for the ancient army size and casualty figures for individual battles used by Oka et al., which suffer from systematic biases designed to magnify the achievements of the historian's own culture. This is clearly illustrated by the main battles of Alexander the Great against the Persians, in which Alexander's forces, although greatly outnumbered, are supposed to have inflicted hundreds or thousands of times more casualties that they sustained. These issues demonstrate the importance of curation of such data by scholars focused on the relevant time periods and cultures, and we recommend that historians become actively involved in such research.