Polybius (203 BC-120 BC) was a Greek historian of the Mediterranean world, especially the rise of the Roman Republic. He is most valued for his account of the Second and Third Punic Wars between Rome and Carthage. Polybius's account endeavoured to provide a universal history of the period between 220 BC and 146 BC, along with a prologue on Roman history from 264 BC, but unfortunately out of the forty books into which his history is divided, only the first five (covering the period up to 216 BC) survive in total, although there are numerous lengthy fragments from the rest of the book. Although not impartial, he was not a Roman and his writings were intended for his fellow Greeks. Livy used him as a reference. Polybius often had excellent sources. He even befriended the younger Scipio Africanus, the famous adopted grandson of the famous general who defeated the Carthaginans in the Second Punic War by routing them from Spain and then defeating Hannibal himself in Africa at the Battle of Zama. The younger Scipio eventually invaded Carthage and forced them to surrender unconditionally. In a classic story of human behavior, Polybius captures it all: Nationalism, Racism, duplicitous politics, horrible battles, brutality, etc.; along with, loyalty, valor, bravery, intelligence, reason and resourcefulness. With his eye for detail and characteristic critically reasoned style, Polybius provided a unified view of history rather than a chronology.
Polybius was responsible for a useful tool in cryptography which allowed letters to be easily signalled using a numerical system. This idea lends itself to cryptographic manipulation.