Polybius was a Greek historian of the Mediterranean world famous for his book called The Histories or The Rise of the Roman Empire, covering the period of 220 BC to 146 BC.

Personal experiences
As the former tutor of Scipio Aemilianus , the famous adopted grandson of the famous general Scipio Africanus, Polybius remained on terms of the most cordial friendship and remained a counselor to the man who defeated the Carthaginians in the Third Punic War. The younger Scipio eventually invaded Carthage and forced the Carthaginians to surrender unconditionally.

Polybius was a member of the governing class, with first-hand opportunities to gain deep insight into military and political affairs. His political career was devoted largely towards maintaining the independence of the Achaean League. As the chief representative of the policy of neutrality during the war of the Romans against Perseus of Macedonia, he attracted the suspicion of the Romans, and was one of the 1000 noble Achaeans who in 166 BC were transported to Rome as hostages, and detained there for seventeen years.

In Rome, by virtue of his high culture, he was admitted to the most distinguished houses, in particular to that of Aemilius Paulus, the conqueror in the First Macedonian War, who entrusted him with the education of his sons, Fabius and the younger Scipio. Through Scipio's intercession in 150 BC, Polybius obtained leave to return home, but in the very next year he went with his friend to Africa, and was present at the capture of Carthage that he described.

After the destruction of Corinth in the same year, he returned to Greece and made use of his Roman connections to lighten the conditions there; Polybius was entrusted with the difficult task of organizing the new form of government in the Greek cities, and in this office gained for himself the highest recognition.

The succeeding years he seems to have spent in Rome, engaged on the completion of his historical work, and occasionally undertaking long journeys through the Mediterranean countries in the interest of his history, more particularly with a view to obtaining first-hand knowledge of historical sites. It also appears that he sought out and interviewed war veterans in order to clarify details of the events he was writing about, and was given access to archival material for the same purpose. After the death of Scipio he returned once again to Greece, where he died at the age of eighty-two, from a fall from his horse.

As historian
Livy used him as a reference and Polybius had excellent sources. Polybius narrated events which came within his own experience. He is one of the first historians to attempt to present history as a sequence of causes and effects, based upon a careful examination of tradition, conducted with keen criticism; partly also upon what he had himself seen, and upon the communications of eye-witnesses and actors in the events.

In a classic story of human behavior, Polybius captures it all: nationalism, xenophobia, 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.

Considered by some to be the successor of Thucydides as far as objectivity and critical reasoning, and the forefather of scholarly, painstaking historical research in the modern scientific sense. According to this view, his work sets forth the course of occurrences with clearness, penetration, sound judgment and, among the circumstances affecting the result, lays especial stress on the geographical conditions. It belongs, therefore, to the greatest productions of ancient historical writing. The writer of the Oxford Companion to Classical Literature (1937) praises him for his "earnest devotion to truth" and for his systematic seeking for the cause of events.

Recently Polybius's writing has come under more critical assessment. In Peter Green's view (Alexander to Actium) he is often partisan, aiming to justify his and his father's careers. He goes out of his way to portray the Achean politician Callicrates in a bad light, leading the reader to suspect that this is due to Callicrates being responsible for him being sent to Rome as hostage.

More fundamentally he, as first hostage in Rome, then client to the Scipios and then finally as collaborator with Roman rule after 146 BC, is not free to express his true opinions. Green suggests that we should always keep in mind that he was explaining Rome to a Greek audience and that further of the need to convince his fellow countrymen of the necessity of accepting Roman rule which he believed as inevitable. Nonetheless, for Green, Polybius's histories remain invaluable and the best source for the era he covers.

Cryptography
Polybius was responsible for a useful tool in telegraphy which allowed letters to be easily signaled using a numerical system. This idea also lends itself to cryptographic manipulation and steganography. This was known as the "Polybius square", where the letters of the alphabet were arranged left to right, top to bottom in a 5 x 5 square, (when used with the modern 26 letter alphabet, the letters "I" and "J" are combined). Five numbers were then aligned on the outside top of the square, and five numbers on the left side of the square vertically. Usually these numbers were arranged 1 through 5. By cross-referencing the two numbers along the grid of the square, a letter could be deduced.

Influence
Polybius was not especially admired by his contemporaries, to whom his lack of high Attic style was seen as a detriment. Later Roman authors writing on the same period, Livy and Diodorus especially, adapted much of his material for their own uses and followed his work extensively. As the Roman position was cemented in Europe, however, Polybius began to decline in popularity. Tacitus sneered at his description of the ideal mixed constitution, and later Imperial writers were generally ignorant of him. Polybius lived on in Constantinople, although in something of a mangled form, in excerpts on political theory and administration.

Nonetheless, it was not until the Renaissance that Polybius' works resurfaced in anything more than a fragmentary form. His works appeared first in Florence. Polybius gained something of a following in Italy, although poor Latin translations of his work hampered proper scholarship on his work, where he contributed to historical and political discussion. Machiavelli appears to have been familiar with Polybius when he wrote his Discourses. Vernacular translations, in French, German, Italian and English, first appeared in the sixteenth century.

Polybius' political beliefs have had a continuous appeal to republican thinkers, from Cicero, to Charles de Montesquieu, to the Founding Fathers of the United States. Since the Enlightenment, Polybius has generally held most appeal to those interested in Hellenistic Greece and Early Republican Rome, and his political and militarial writings have lost influence in academia. More recently, thorough work on the Greek text of Polybius and his historical technique has increased academic understanding and appreciation of Polybius as a historian. According to Edward Tufte, Polybius was also a major source for Charles Joseph Minard's figurative map of Hannibal's overland journey into Italy during the Second Punic War.