Arrian was a Greek historian and military commander who lived in the 2nd century AD. He is best known for his work, the "Anabasis of Alexander," which details the life and conquests of Alexander the Great. Arrian's writings are considered valuable historical sources because he relied on earlier accounts and firsthand experiences from those who accompanied Alexander. In addition to his historical works, Arrian served as a Roman official and wrote on various subjects, including philosophy and military tactics. His writings reflect a blend of Greek and Roman culture, showcasing the influence of both civilizations during his time.