knowledge of applied geometry and use of the surveying instrument called the dioptra. Hero of Alexandria's manuscripts suggest that the dioptra could be used as a level and for measuring elevations, distances, and angles. Heron of Byzantium spoke about its use in siege warfare, showing that it could estimate distances and the required sizes of siege engines. Edition Sullivan, Dennis F., ed. (2000). Siegecraft: Two Tenth-Century Instructional Manuals by "Heron of Byzantium". Dumbarton Oaks Studies XXXVI. Washington, DC: Dumbarton Oaks Research Library and Collection. . Sources 10th-century Byzantine writers Medieval Greek military writers 10th-century Byzantine people Unidentified people