Papinian, considered for centuries the greatest Roman jurist, writes his most influential works — 37 books of Quaestiones and 19 of Responsa — as praetorian prefect under Septimius Severus. In 212, after Caracalla ordered the murder of his brother Geta, Papinian refuses to draft a public justification of the crime before the Senate; he is executed by imperial order. His legendary reply: "accusing an innocent man who has been murdered is a second act of murder." His writings become a required reference for law students (third-year students were called Papinianistae) and, together with Gaius, Ulpian, Paul, and Modestinus, one of the five authorities recognized by Theodosius II's Law of Citations (426).