Glancing back over the history of war from the date of the Messenian War to the 4th century A.D., a period of i,000 years, a similar tactical evolution can be traced in both the Grecian and Roman worlds. First we are confronted by an infantry period, the phalanx and early legion. Then contact with the Persian cavalry and Numidian horse points to the value of the rear at tack. The art of war under Alexander, Hannibal and Scipio, all great cavalry and infantry leaders, suddenly advances by leaps and bounds, because they understand how to develop cavalry pressure from infantry resistance. Almost immediately after their death the art sinks to a low level, since this balance between the stable and mobile elements in tactics is not maintained. When the industrial epoch is entered, in the 3rd century B.C. in the case of the Hellenistic world, and in the I st century B.C. in that of the Roman, artillery came to the fore, and though under able gen erals it is used offensively to develop the attack, more often than not it is used defensively to beat back an attacker. The will to clinch with an enemy is lost, and the result is that though military organization, especially in the Eastern empire, is of a high order, the loss in the spirit of the offensive deprives tactics of its soul, and the art of war enters its decadence.
Though it is obviously not possible to date the initiation, or close, of any tactical period throughout the Christian age, that is from about the close of the 4th century to present times, three great tactical cycles can be traced. The first is the cavalry cycle, which may be said to open with the battle of Adrianople (q.v.) in 378 B.C. and close with that of Agincourt (q.v.) in 1415. The sec ond, the infantry cycle, though its origins are more indeterminable, next follows, reaches its apex under Frederick and Napoleon, and then steadily loses ground during the 19th century. In the World War of 1914-1918, it is definitely replaced by an artillery cycle, the origins of which reach back to the 16th century, and become plainly manifest during the Seven Years' War and the Napoleonic Wars. These three cycles will now be examined with the ultimate aim of forecasting the tactical tendencies of the age in which we live, and those of its immediate future.
The Late Roman and Early Gothic Cavalry.—Cavalry is pre-eminently the offensive arm, not because it can charge an in fantry line, but because it can circumvent it, and either attack it in rear, or starve it into surrender by capturing its baggage train. Infantry can normally withstand the cavalry charge, con sequently, when supported by cavalry, they, if efficiently armed, are invaluable as a "mobile fortress"—a pivot for cavalry man oeuvre, and if they in their turn are protected by artillery, which cannot protect itself, tactics flourish as a high art. After the bat tles of Carrhae (53 B.c.) and Pharsalus (48 B.c.) though there
was a steady increase in Roman cavalry, there was also a steady deterioration in Roman infantry. Under Diocletian (245-313) cavalry rose from one-tenth to one-third of the infantry and numbered some i6o,000; but this great mass of horse was with drawn from the infantry, and by being formed into a frontier guard lost its offensive spirit, and generally speaking was no match for the barbarian horsemen who in the 3rd century invaded the empire.
The decline in the value of the Roman infantry which was due to social reasons as well as military, left the defensive Roman cav alry without a base to meet the offensive Gothic horsemen whose first irruption took place in A.D. 248. Thirty years later, the em peror Valens met the Goths under Fritigern at Adrianople ; his cavalry were routed and his legionaries surrounded and destroyed. In this battle the Romans are reputed to have lost 40,00o men. Though at times such as the battle of Taginae (q.v.) in 552, which resembles Crecy (q.v.) in 1346, and the battle of the Sarno (554), which resembles Cannae, such eminent generals as Narses succeed in wonderful combinations of infantry and cavalry, and of fire and shock tactics, the use of cavalry becomes more and more general. In 535, Belisarius in Africa won the decisive vic tory of Tricameron (q.v.) over the Vandals purely by cavalry, and a few years later we find that he has so little use for his in fantry that he mounted them to serve as dragoons.