Was reading the thread on Roman organisation on the GW forums (forii?) and was stunned at the misinformation...apparently loads of people try to structure their armies like Romans. Anyway, for the recors, if its ueful, here it is. (Dunno if this should be here or in SM, but start here...)
1. Roman army lasted c 1,000 years, and the Eastern Roman (aka Byzantine) lasted another 1,000. The stuff below is for teh Romans, Byzantine armies were (usually) mainly cavalry, not infantry.
2. There were many changes in this time. The best known to most people are the Republican armies facing Hannibal, the early Empire of Juliues Caesar, British conquest etc, and the Late Roman armies of Constantine etc.
3. The Republican Roman army (c 200 BC) had Legions divided into 3 basic troops types - velites (light troops), hastati and principes (basically legionaries, the terms describe earlier days) and triarii (heavily armoured veterans, kept in reserve.) A full Roman consular army consisted of 4 legions, 2 Roman and 2 Latin plus cavalry and missile troops, usually allies or mercenaries. Each Legion has 10 maniples of Hastati, 10 of Principes, each of 120 men, 10 maniples of 60 triarii each, and 1200 Velites split up as needs. Each Maniple has 2 Centurions, 2 Optios, and 2 Signifers (standard bearers). A Maniple of Principes, Hastati and Triarii is sometimes combined into a Cohort. Each Legio has 10 turmae of 30 cavalry, each commanded by a Decurion.
4. The Early Empire (c 0 AD) has Legions divided into 10 Cohorts of 480, except the first Cohort which is c 800 men. The light troops roles are now done by Auxilia, the Triarii are blended into the Legio. Each Cohort has 6 Centuries, commanded by a Centurion, assisted by an Optio. 2 Centuries are grouped into a Maniple for admin purposes. Each Century has 10 Contubernia of 8 men, commanded by a Decanus. There are at least as many Auxilia in a standard army as Legionaries, each Auxilia Ala (wing) is structured like a Cohort, and Cavalry Alae have 16 Turmae of 30 men commanded by a Decurion.
5. The Late Empire (c 400AD) has Legiones, not Legios, of about 1,000- 1,200 men. Legione org is much more fluid, but is believed to be usually 6 Ordines, each of 2 Centuries, each of 100 men grouped in 10 Contubernia of 10 men. Auxilia infantry units are of 3 Ordines, and are about 500-600 men. Cavalry units are half that size. the "rapid response" troops are called Legio or Auxilia Palatina, the garrison or local troops are called Comitatensis. Local (border) Militia are called Limites or Milites.
For the Record, Sparta organised her Hoplites (soldiers who carried the Hoplon shield) into Morai of 600 men, each made up of 4 lochai of c 150 men (144 troops and 6 officers), divided into 2 pentekostys, each of 2 enomotiai, each of 36 men. A phalanx is the Greek term for a close formation of heavy infantry, typically 4 - 8 deep in the Spartan army, 8 - 16 deeep in Alexander's Macedonians. Light missile troops are provided by Psiloi, and a medium weight, jack of all trades trooper emerged later called a Peltast.
Hope that helps......
