The Roman Empire (Imperium Romanum) was a civilization which ruled over much of Western Eurasia ruled from the Italian City of Roma. Technically the Roman Empire existed from 27BCE to 476CE (1453 if you include the subsequent Byzantine Empire), although the term also is used to informally refer to the preceeding Roman Republic, which existed for some 500 years previously. The Roman Empire was for its time highly advanced and developed; after its collapse, European civilization fell back for centuries technologically.
Roman Society was stratified on class lines, with a number of tiers based off a number of factors including wealth, ansestory and integration into roman society. Leaving aside the Imperial Throne, at the top was the patrician class, who owned large amounts of land or had income through trade connections and owning centers of manufacturing (the latter two being seen as less prestigious than land ownership) and were usually versed in Roman Law. Beneath them where the Plebs, who were lower classes of artisans, workers and farmers that still held citizenship. These people were usually the clients of Patrician patrons, in exchange for supporting their Patron politically and providing various services when needs, the patron would represent his clients in court, offer financial support and help them in business deals. At the bottom of Roman Society was a large population of Slaves, making up as much as fifty percent of the Roman Population employed in every job from mine workers to administrators in the Roman Government. Many slaves were eventually granted freedom by their masters, either as a gift by a beneficent master or by buying their freedom. Usually freed slaves became the clients of their former masters.
In addition to the citizen classes and slaves existed various subject peoples, including denizens of Roman client kingdoms and people who lived in newly conquered areas that had not been enslaved. These peoples could be wealthy and prominently local, but were usually at a major social disadvantage due to their lack of citizenship. Fortunately for these subject peoples the Romans opened a number of paths to citizenship and would occasionally elevate entire regions to Roman Citizenship as a means of integrating these populations.
The Roman Military
The Roman military varied from period to period, as the Romans adjusted their forces and adopted new technologies and strategies. The first Roman armies were armed and fought in a manner similar to that of Greek Hoplites armed with spears, although this gradually gave way to swordsmen in forces that were divided along class lines. In this early period most Roman soldiers were of a certain class able to afford weapons, armor, and food on campaign. As part of their civic duty, men of said class were required to serve in the Roman Army during times of war. The most notable development of the Roman military was the reforms of Gaius Marius in 107 BCE, who professionalized the Roman army into a standing force.
Roman forces after the Marian Reforms were divided into two forces:
- Legions: Recruited from the citizen classes, Legionaries were heavy infantry armed with rectangular shields, swords (Gladius), and javelins (Pilum). Each Legion had at maximum strength 5,240 soldiers. Roman Legions excelled against enemy infantry formations, but were often poorly suited. Each Legion would have a small force of light cavalry attached to it to serve as scouts and to pursue retreating forces. Roman Legions were sub divided into units called centuries (overseen by Centurions) and were lead by officers known as Legates.
- Auxiliaries: Auxiliaries consisted of non-citizen troops recruited from provinces. Often these would fill in gaps that Legionaries lagged in, such as archers and cavalry. To prevent revolt, Auxiliaries were generally stationed well away from their home territory. Completion of a term of service in the auxiliaries usually ended with being granted full citizenship.
At peak strength, the Roman Military had about a force of 500,000 soldiers (approximately 200,000 legionaries and 300,000 auxiliaries) and was by far the largest arm of the Roman Government and where it spent most of its money. In addition to fighting, Military forces would do various odd jobs required by the roman state (building roads and fortifications, working on various public works, enforcing law in the provinces, etc). In the Imperial Period, the Legions would play a major role in imperial politics, installing their Legates as Emperors and deposing Emperors who were short on payment. Towards the latter years, the Roman military became increasingly dependent on unreliable foreign mercenaries for defense, which contributed to the fall of the Empire.
The Roman Empire in Debates
The Roman Empire comes up quite often in fantasy debates and is among the favorite targets of alternate history scenarios. Roman equipment and tactics are well documented. Roman Legionaries are generally regarded as formidable soldiers by pre-modern standards and generally fair well when faced with most other infantry heavy foes, but they are poorly suited for combat against latter heavy cavalry and cavalry archers.
Thanas is quite knowledgeable about this civilization. If you want questions answered about rome, he's the guy to turn to.