Roman army

• 1. Origins And Early Development

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  In 550 BC, King Servius Tullius instituted a universal levy of eligible adult male citizens. This development coincided with the introduction of heavy armour for most infantrymen. Before this moment, Rome relied on clan-based war-bands that only coalesced into a united force during serious external threats. The standard levy probably numbered 9,000 men consisting of 6,000 heavily armed infantry and 2,400 light-armed infantry. A small group of 600 light cavalry also participated in these early campaigns. When kings were replaced by two annually elected praetores around 500 BC, the levy remained the same size but divided equally between them. Each praetor commanded one legion of 4,500 men. These early forces fought in Greek-style phalanx formations during large set-piece battles. Most fighting consisted of small-scale border raids and skirmishing instead. Romans fought in their basic tactical unit called the centuria containing 100 men. Separate clan-based forces existed until at least 358 BC under Praetors authority. In 493 BC Rome concluded a perpetual treaty of military alliance known as the Foedus Cassianum with other Latin city-states. This treaty provided for each party to provide an equal force for campaigns under unified command.

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• 2. The Marian Transformation

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  Gaius Marius assumed command in 107 BC during a period when maniples were gradually phased out as the main tactical unit. Large cohorts used in allied armies replaced them in this process. The Republican army did not maintain standing or professional military forces before this era. Conscripts served only for each campaigning season and disbanded thereafter. Service in legions was limited to property-owning Roman citizens aged 16 to 46 years old. Elders, vagrants, freedmen, slaves and convicts were excluded from the military levy except in emergencies. During the Second Punic War extreme manpower needs forced the army to ignore minimum property requirements. Many volunteers drawn from the poorest social class served much longer periods than before. These volunteers were willing to serve beyond the six consecutive years limit imposed by law. The standard levy doubled during Samnite Wars to four legions totaling approximately 18,000 Roman troops. Four allied alae of similar size accompanied these forces. The army campaigned exclusively outside Italy after Carthage fell in 201 BC. Men remained away from their home plots of land for many years at a stretch. They received large amounts of booty shared after victories in rich eastern theatre. Disaffection among Rome's Italian allies led to mass revolt known as Social War between 91 and 88 BC. Grant of Roman citizenship to all Italians ended Polybian army dual structure.

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• 3. Imperial Structure And Auxilia

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  Augustus ruled from 30 BC until 14 AD transforming legions into all-volunteer units serving standard 25-year terms. Conscripted service occurred only in emergencies under this new system. Legionary personnel increased to approximately 5,500 when First Cohort size doubled in later 1st century. Augustus established auxilia corps recruiting from peregrini non-citizen inhabitants comprising about 90% of empire population in 1st century. Auxiliaries provided virtually all cavalry heavy and light plus archers and other specialists. Units organized in approximately 500-strong formations called numeri included all-infantry and all-cavalry types. Around 80 AD minority auxiliary regiments doubled in size. After 68 AD auxiliaries became largely volunteer corps with conscription resorted to only in emergencies. Minimum service term required 25 years though many served longer periods. On completion of minimum term auxiliaries awarded Roman citizenship carrying important legal fiscal and social advantages. By end of Augustus reign imperial army numbered some 250,000 men equally split between legionaries and auxiliaries. Numbers grew to peak of about 450,000 by 211 containing 33 legions and c. 400 auxiliary regiments. From peak numbers underwent steep decline by 270 due to plague and losses during multiple major barbarian invasions. Diocletian restored numbers to early 2nd-century level of c. 400,000 after empire borders settled on Rhine-Danube line.

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• 4. Crisis And Late Empire Reforms

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  Emperor Diocletian took power in 284 initiating significant transformation of the Principate army structure. Army of 4th century heavily dependent on conscription and soldiers more poorly remunerated than in 2nd century. Barbarians from outside empire supplied much larger proportion of late army recruits compared to earlier centuries. Size of 4th-century army controversial with estimates ranging half size again or twice as large as predecessor. Contemporary historians view late army no larger than its predecessor under Diocletian at c. 390,000. Main structural change established large armies accompanying emperors generally based away from frontiers. Primary function deterred usurpations rather than defending borders directly. Legions split up into smaller units comparable in size to auxiliary regiments of Principate period. Legionary armour and equipment abandoned in favour of auxiliary equipment adopted by infantry. Cavalry acquired reputation for incompetence and cowardice following three major battles mid-4th century. Infantry retained traditional reputation for excellence throughout this turbulent era. Many existing border forts upgraded to make them more defensible while new forts constructed with higher defensive specifications. Debate continues whether army adopted defence-in-depth strategy or continued forward defence posture. Practice keeping large armies best troops interior deprived border forces sufficient support against barbarian incursions.

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• 5. Byzantine Evolution And Decline

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  Battle of Manzikert in 1071 destroyed professional tagmata core of Byzantine army during 11th century. Alexios I Komnenos could manage field only 500 soldiers from Empire's professional forces in 1091 nadir. These formed nucleus added armed retainers relatives nobles enrolled army substantial aid allied Cumans winning Battle Levounion against Pechenegs. New force contained formidable guards units Varangians Athanatoi heavy cavalry stationed Constantinople Vardariotai Archontopouloi recruited sons dead officers foreign mercenary regiments provincial professional soldiers. Provincial troops included kataphraktoi cavalry Macedonia Thessaly Thrace Trebizond archers Black Sea coast Anatolia. In 1097 Byzantine army numbered around 70,000 men altogether. Field army rose to 40,000 men by end Manuel I reign after starting at 20,000 under Alexios. Palaiologan army refers military forces late 13th century final collapse mid 15th century House Palaiologoi. Army direct continuation Nicaean army fractured component formidable Komnenian army. Under Michael VIII role took increasingly offensive while naval forces boosted include thousands skilled sailors some 80 ships. By c. 1350 following destructive civil war outbreak Black Death Empire no longer capable raising troops supplies maintain them. Last decisive battle fought Palaiologan army 1453 when Constantinople besieged fell the 29th of May. Last isolated remnants Byzantine state conquered by 1461.