I need to summarize Polybius' Histories.
The Histories is a work of Roman history, written in Greek by an eye-witness of the political and martial world of the second century.
Polybius had ample interaction with and knowledge of the Romans. He was an Achaean statesman when Rome’s presence was a real force in the Greek world, and subsequently he was one of the thousand who was taken to Rome when the Romans began to suspect the loyalty of the Achaeans after their war with Perseus, the King of Macedonian in 167 BC. During this time (167-150), Polybius stayed in Rome and became associated with the Roman elite. He also became the tutor of Scipio Aemilianus and subsequently accompanied him to Africa and Spain (150 BC?). He was also present at the destruction of Carthage (146 BC). In short, Polybius was an eyewitness of the second century and an insider of Roman elite culture. It is no wonder that the great Roman annalist, Livy followed him at times in his own work.
The content of the work was how the Romans became the superpower of the Mediterranean world in such a short period of time. In light of this theme, Polybius writes much about the various conflicts Rome had with the Greek East. He also spends considerable time writing of Rome's conflict with Carthage. Finally and perhaps most importantly Polybius write of the superiority of the Roman constitution.