Editing Roman Empire (section)

===Military===
{{Main|Imperial Roman army|Late Roman army|Structural history of the Roman military}}
[[File:Palestra grande di pompei, affreschi di Moregine, terzo triclinio, IV stile, epoca neroniana, 07 vittoria con tripode.jpg|thumb|upright|Winged [[Victoria (mythology)|Victory]], ancient Roman fresco of the Neronian era from [[Pompeii]]]]
[[File:Roman Empire 125.png|thumb|upright=1.35|The Roman Empire under [[Hadrian]] (ruled 117–138) showing the location of the Roman legions deployed in 125 AD]]

After the [[Punic Wars]], the Roman army comprised professional soldiers who volunteered for 20 years of active duty and five as reserves. The transition to a professional military began during the late Republic and was one of the many profound shifts away from republicanism, under which an army of [[conscripts|conscript citizens]] defended the homeland against a specific threat. The Romans expanded their war machine by "organizing the communities that they conquered in Italy into a system that generated huge reservoirs of manpower for their army".<ref>{{Cite book |last1=Tignor |first1=Robert |url=https://archive.org/details/worldstogetherwo03alti |title=Worlds Together, Worlds Apart: The History of the World |last2=Adelman |first2=Jeremy |date=2011 |publisher=W.W. Norton & Company |isbn=978-0-3939-3492-2 |edition=3rd |page=[https://archive.org/details/worldstogetherwo03alti/page/n313 262] |display-authors=1 |url-access=limited}}</ref> By Imperial times, military service was a full-time career.{{Sfnp|Edmondson|1996|pp=111–112}} The pervasiveness of military garrisons throughout the Empire was a major influence in the process of [[Romanization (cultural)|Romanization]].{{Sfnp|Bohec|2000|p=9}}

The primary mission of the military of the early empire was to preserve the [[Pax Romana]].<ref>{{Cite book |last=Hekster |first=Olivier J. |chapter=Fighting for Rome: The Emperor as a Military Leader |date=2007 |title=Impact of the Roman Army (200 BC–AD 476) |publisher=Brill |page=96}}</ref> The three major divisions of the military were:
* the garrison at Rome, comprising the [[Praetorian Guard]], the ''[[cohortes urbanae]]'' and the ''[[vigiles]]'', who functioned as police and firefighters;
* the provincial army, comprising the [[Roman legions]] and the auxiliaries provided by the provinces (''[[auxilia]]'');
* the [[Roman navy|navy]].
[[File:042 Conrad Cichorius, Die Reliefs der Traianssäule, Tafel XLII.jpg|thumb|upright=1.6|Relief panel from [[Trajan's Column]] in Rome, showing the building of a fort and the reception of a [[Dacia]]n embassy]]

Through his military reforms, which included consolidating or disbanding units of questionable loyalty, Augustus regularized the legion. A legion was organized into ten [[Cohort (military unit)|cohorts]], each of which comprised six [[centuria|centuries]], with a century further made up of ten squads (''[[Contubernium (Roman army unit)|contubernia]]''); the exact size of the Imperial legion, which was likely determined by [[military logistics|logistics]], has been estimated to range from 4,800 to 5,280.<ref>{{Cite journal |last=Roth |first=J. |date=1994 |title=The Size and Organization of the Roman Imperial Legion |journal=Historia |volume=43 |issue=3 |pages=346–362}}</ref> After Germanic tribes wiped out three legions in the [[Battle of the Teutoburg Forest]] in 9 AD, the number of legions was increased from 25 to around 30.{{Sfnp|Goldsworthy|2003|p=183}} The army had about 300,000 soldiers in the 1st century, and under 400,000 in the 2nd, "significantly smaller" than the collective armed forces of the conquered territories. No more than 2% of adult males living in the Empire served in the Imperial army.{{Sfnp|Morris|Scheidel|2009|p=196}} Augustus also created the [[Praetorian Guard]]: nine cohorts, ostensibly to maintain the public peace, which were garrisoned in Italy. Better paid than the legionaries, the Praetorians served only sixteen years.<ref>{{Cite book |last=Penrose |first=Jane |quote=Section 3: ''Early Empire 27 BC–AD 235'' |date=2005 |title=Rome and Her Enemies: An Empire Created and Destroyed by War |publisher=Bloomsbury US |isbn=978-1-8417-6932-5 |page=183 |chapter=9: ''The Romans''}}</ref>

The ''auxilia'' were recruited from among the non-citizens. Organized in smaller units of roughly cohort strength, they were paid less than the legionaries, and after 25 years of service were rewarded with [[Roman citizenship]], also extended to their sons. According to [[Tacitus]]<ref>[[Tacitus]] ''[[Annals (Tacitus)|Annales]]'' IV.5</ref> there were roughly as many auxiliaries as there were legionaries—thus, around 125,000 men, implying approximately 250 auxiliary regiments.{{Sfnp|Goldsworthy|2003|p=51}} The [[Roman cavalry]] of the earliest Empire were primarily from Celtic, Hispanic or Germanic areas. Several aspects of training and equipment derived from the Celts.<ref>{{Cite journal |last=Connolly |first=Peter |date=1986 |title=A Reconstruction of a Roman Saddle |journal=Britannia |volume=17 |doi=10.2307/526559 |pages=353–355 |jstor=526559 |s2cid=164155025}}; {{Cite journal |last1=Connolly |first1=Peter |last2=Van Driel-Murray |first2=Carol |date=1991 |title=The Roman Cavalry Saddle |journal=Britannia |volume=22 |doi=10.2307/526629 |pages=33–50 |jstor=526629 |s2cid=161535316}}</ref>

The [[Roman navy]] not only aided in the supply and transport of the legions but also in the protection of the [[Limes (Roman Empire)|frontiers]] along the rivers [[Rhine]] and [[Danube]]. Another duty was protecting maritime trade against pirates. It patrolled the Mediterranean, parts of the [[Atlantic|North Atlantic]] coasts, and the [[Black Sea]]. Nevertheless, the army was considered the senior and more prestigious branch.{{Sfnp|Goldsworthy|2003|p=114}}