Which written records did Polybius consult for the Histories?

For his Histories, Polybius utilized a variety of written records, though he rarely named the specific authors he consulted for the main portion of his work covering the period from 220 BCE onward. His research methods included:1

• Private Correspondence: He accessed personal letters, such as those from Publius Cornelius Scipio regarding the capture of New Carthage and correspondence from Scipio Nasica concerning the Third Macedonian War.1
• Official Archives: He likely consulted the Achaean record office and utilized Roman records, such as the treaty between Carthage and Philip V of Macedonia.1
• Inscriptions: He gathered specific data, such as details regarding Hannibal’s troop formations in Italy, from an inscription located in the Temple of Juno on the Lacinian promontory.1
• General Historical Works: For his introductory books (covering 264–220 BCE), he relied on various Greek and Roman writers.1

While he valued these records, Polybius considered the questioning of witnesses and oral sources to be the most vital component of a historian’s task.1