Mnaseas is reckoned to have been a pupil of a scholar who was chief librarian at what library?
Eratosthenes Eratosthenes of Cyrene ( ; Greek: Ἐρατοσθένης ὁ Κυρηναῖος , ] ;  – ) was a Greek mathematician, geographer, poet, astronomer, and music theorist. He was a man of learning, becoming the chief librarian at the Library of Alexandria. He invented the discipline of geography, including the terminology used today.
Tacitus Publius (or Gaius) Cornelius Tacitus ( ; ] ;  56 AD –  120 AD ) was a senator and a historian of the Roman Empire. The surviving portions of his two major works—the "Annals" and the "Histories"—examine the reigns of the Roman emperors Tiberius, Claudius, Nero, and those who reigned in the Year of the Four Emperors (69 AD). These two works span the history of the Roman Empire from the death of Augustus, in 14 AD, to the years of the First Jewish–Roman War, in 70 AD. There are substantial lacunae in the surviving texts, including a gap in the "Annals" that is four books long.