Roman Army Ranks - Hierarchy
The basic hierarchy of the Roman Army ranks was as follows:

• The General / Dux / Imperator / Commander
• The Lieutenants or Legates (legati) who frequently commanded separate legions
• The Quaestor who was charged with the care of the military chest and the supplies
• The Body-guards (cohors praetoria) of the senior officers
• The military Tribunes (tribuni militum)
• The Captains, or Centurions
• Immunes - Soldiers with special skills
• Standard bearers
• Evocati - Veteran soldiers
• Beneficiarii - the orderlies
• Conicen - The musicians
• Munifex - The Roman Soldiers - the lowest ranks equivalent to privates

Roman Army Ranks
The following info provides a list and definition of the Roman Army Ranks found in a legion. The number of soldiers in a legion was not absolutely fixed. The numbers of soldiers in a the legion at first contained 3000 soldiers, increasing to 4000 or 4200 infantry during the Punic Wars and eventually the numbers varied from 5000 to 6200, generally approaching to the higher limit. Amid all the variations with regard to the infantry, 300 horsemen formed the regular complement of the legion. The following table provides a list and definition of the Roman Army Ranks found in a legion: 

• Adscripticius: Adscripticius - an additional soldier of the Roman Republic who served to fill the places of those who were killed or disabled

• Aquilifer : Aquilifer carried the legionary eagle.

• Armicustos: Armicustos was a quartermaster - tasked with the administration and supply of weapons

• Auxiliaries: Auxiliaries (from Latin: auxilia meaning "supports") formed the standing non-citizen corps

• Ballistarius: Ballistarius was an artillery operator.

• Beneficiarii : Beneficiarii - orderlies who performed various services for the higher army officers

• Cataphractarii: Cataphractarii were heavily armed and armoured cavalrymen deployed in the 2nd Century AD

• Centurion: A Centurion was an important role in the Roman Army Ranks. A centurion had 100 men in his command

• Centuriones exercitatores: Centuriones exercitatores were the training officers for the cavalry

• Cohortes equitates: Cohortes equitates were the mixed cohorts of cavalry and infantry

• Conicen (cornicines): A Conicen was the horn-blower in the Roman Army ranks. There was one to every century.

• Cornicularius: Cornicularius An administrative officer within a legion

• Decanus: Decanus was the first rank that a legionary could be promoted to. Similar to a modern-day Sergeant

• Discentes signiferorum: Discentes signiferorum A trainee standard bearer

• Draconarius : Draconarius was a Roman cavalry standard bearer

• uplicarius: Duplicarius was an officer of the Roman legions receiving double the basic pay.

• Equites: Equites - Roman citizen horse troops drawn from the Roman equestrian class.

• vocati: Evocati were soldiers who had served their full time but had re-enlisted at the general's request - veteran volunteers

• Extraordinarii: Extraordinarii Soldiers set aside for special backup services. This force usually contained 20% of the infantry and 33% of the cavalry

• Hastiliarius: Hastiliarius was a weapons instructor

• Hastati : Hastati (raw troops). The soldiers of the first line consisted of youths and were armed with the hasta, or spear

• Imaginifer: Imaginifer: Carried the Standard bearing the three dimensional image of the Emperor

• Immunes: Immunes were soldiers who had special skills and who were "immune" from combat duty and fatigues through having a more specialist role within the army

• Lancearii : Lancearii - Spear armed mail clad field troopers

• Legate (Legatus or Legatus legionis): Legatus or Legatus legionis A legatus (often anglicized as legate) was a general in the Roman army,

• Libritors: Libritors were artillerymen who operated siege engines such as the onager

• Miles or Miles Gregarius: Miles or Miles Gregarius - The basic private level foot soldier

• Munifex: Munifex The lowest rank in a legion. Equivalent to a private

• Optio: Optio A legion centurion's second in command

• Peditatus : Peditatus - a term referring to any infantryman

• Pilus prior: Pilus prior A high ranking officer within a manipuli who also commanded the cohorts

• Praetor: Praetor was the commander of an army

• Prefectus : Prefectus A general term used for the holders of different ranks in the military

• Prefectus castrorum: Prefectus castrorum The third in command in a legion

• Prefectus equitatius: Prefectus equitatius An officer commanding a unit of cavalry

• Prefectus fabrorum: Prefectus fabrorum An officer who had responsibility for the craftsmen supplying services to the military. Blacksmiths, metal workers etc

• Primus Pilus: Primus Pilus: Legion Commander

• Principes : Principes (trained troops) composed of experienced men

• Quaestionarius : Quaestionarius - an interrogator or torturer.

• Sagittarii : Sagittarii - archers, including horse-riding auxiliary archers recruited mainly in the Eastern Empire and Africa

• Scorpionarius: Scorpionarius was an artilleryman operating a scorpion artillery weapon

• Signifier: The Signifier carried the Century's standard (signum) into battle and was also the treasurer for the Century. Senior Officer in a Century

• Socii : Socii - Conscripts

• Triarii : Triarii (veterans) Experienced soldiers were armed with the pilum, four and a half feet long, of wood, with a barbed head of iron, so that the whole length of the weapon was six feet nine inches.

• Tribune (Tribunus): Tribune (Latin:Tribunus) One of six assistants to a legion commander, the Primus Pilus. Usually a young senator learning the basics for his career

• Tribunus Cohortis: Tribunus Cohortis: Commander of a Cohort military unit.

• Tribunus Cohortis Urbanae: Tribunus Cohortis Urbanae: Urban cohort commander.

• Tubicines: The trumpeters

• Velites : Velites The light soldiers. Unlike the Hastaii, they did not have full armour, although they did have a helmet and a shield. They were also armed with a sword, but had a only a short javelin as opposed to a pilum.

• Venator: Venator - a hunter (a type of immunes)

• Vexillarius: The bearer of the vexillum standard