 Al-Zahrawi also wrote the "At-Taṣrīf limanʿajazʿan at-Taʾālīf," or "At-Taṣrīf" (“The Method”), which was a 30-part text based on earlier authorities, such as the "Epitomae" from the 7th-century Byzantine physician Paul of Aegina.It was largely composed of medical observations, including what is considered the earliest known description of hemophilia.The 30-volume encyclopedia also documented Zahrawi and his colleagues’ experiences with treatment of the ill or afflicted.