Primary literary sources for Alexander the Great do not exist anymore. There were for example writings of Kallisthenes, Ptolemaios and Aristobul but none remain today. Arrian (his Anabasis) is considered the best secondary source. He used the writings of Kallisthenes, Ptolemaios, Aristobul and Nearchos (who all took part in the conquests of Alexander) for his work. Otherwise there are Plutarch (Parallel Lives, comparing with Caesar), Diodor, Curtius Rufus and Iustin.