The Byzantine Army was the military force of the Byzantine Empire, which existed from the 4th to the 15th century. It evolved from the earlier Roman military and was known for its organization, discipline, and use of advanced tactics. The army included various units, such as heavy cavalry, archers, and infantry, and often relied on mercenaries. The Byzantine Army played a crucial role in defending the empire against various threats, including Persians, Arabs, and Turks. It was also instrumental in expanding the empire's territory during periods of strength, particularly under emperors like Justinian I. The army's strategies and innovations influenced military practices in Europe and beyond.