Aelian (Aelianus Tacticus) was a Greek military writer of the 2nd century A.D., resident at Rome. He is sometimes confused with the Roman writer Claudius Aelianus.

Aelian's military treatise, Taktike Theoria, is dedicated to Hadrian, though this is probably a mistake for Trajan, and the date A.D. 106 has been assigned to it. It is a handbook of Greek, i.e. Macedonian, drill and tactics as practised by the Hellenistic successors of Alexander the Great. The author claims to have consulted all the best authorities, the chief of which was a lost treatise on the subject by Polybius. Perhaps the chief value of Aelian's work lies in his critical account of preceding works on the art of war, and in the fulness of his technical details in matters of drill. Critics of the 18th century—Guichard Folard and the prince de Ligne—were unanimous in thinking Aelian greatly inferior to Arrian, but both on his immediate successors, the Byzantines, and on the Arabs, who translated the text for their own use, Aelian exercised a great influence. The emperor Leo VI incorporated much of Aelian's text in his own work on the military art. The Arabic version of Aelian was made about 1350. In spite of its academic nature, the copious details to be found in the treatise rendered it of the highest value to the army organizers of the 16th century, who were engaged in fashioning a regular military system out of the semi-feudal systems of previous generations. The Macedonian phalanx of Aelian had many points of resemblance to the solid masses of pikemen and the squadrons of cavalry of the Spanish and Dutch systems, and the translations made in the 16th century formed the groundwork of numerous books on drill and tactics. Moreover, his works, with those of Xenophon, Polybius, Aeneas and Arrian, were minutely studied by every soldier of the 16th and 17th centuries who wished to be master of his profession. It has been suggested that Aelian was the real author of most of Arrian's Tactica, and that the Taktike Theoria is a later revision of this original, but the theory is not generally accepted.

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