By this period the Roman Republic had ended its Civil Wars, from which Augustus emerged victorious as Emperor of Rome. Already dominant around the Mediterranean, Rome set about strengthening her grip on areas further North and East engaging in conflicts with many different opponents.
This is the period most people think of when they think of Ancient Rome and her soldiers in their segmented armor with big, curved, rectangular shields. While the legionaries were the core of the Roman Army, there were typically about as many auxiliary troops that fought alongside the Legion. Mainly infantry, or less often cavalry in chainmail shirts with a spear and an oval shield, along with other auxiliaries armed with bows or slings. In both sieges and open battle Romans also typically brought their war engines to bear. As well as troops from within the Empire, the Romans were also known to field tribal troops from outside their borders under native or Roman officers.
Best known from Trajan's Column in Rome, which commemorates Trajan's victory over the Dacians and the incorporation of Dacia into the Empire, the Dacians were a difficult opponent. During the reign of the emperor Domitian the Dacians butchered a Roman army and forced the Romans to negotiate a peace treaty. Famed for their use of the deadly falx, a three foot haft with a sickle like blade on the end, the Dacian warbands also used javelins and spears, supported by archers. The Dacian cavalry was supplemented by troops from the neighboring Sarmatian tribes and included Sarmatian cataphracts - armored men on armored horses.
Part of a Celtic culture that stretched from Ireland all the way across to the Galatians of Turkey, the Gauls occupied France and maintained cultural links with the Ancient British. Gallic and British armies would have a core of infantry warbands composed of warriors with shields, spears or swords, some armored, some not. A few tribesmen would instead be armed with bows or, particularly in Britain, slings. Nobles were better armored and rode horses or, in Britain, chariots. Gaesatae were fanatics who charged into battle naked, relying on their skill at arms and the shock value of their ferocious reputation for protection.
The Sarmatians were a large Iranian confederation that existed in classical antiquity, flourishing from about the 5th century BC to the 4th century AD. Originating in the central parts of the Eurasian Steppe, they were part of the wider Scythian cultures. They started migrating westward around the 4th and 3rd centuries BC and at their greatest extent ranged from the Vistula river to the Volga. Sarmatia covered modern day central and south-eastern Ukraine, southern Russia, the Volga and South-Ural regions, as well as areas of the north-eastern Balkans and around Moldova. In the 1st century AD, the Sarmatians began encroaching upon the Roman Empire in alliance with Germanic tribes until the 3rd century AD when their dominance of the Pontic Steppe was broken by the Germanic Goths. With the Hunnic invasions of the 4th century, many Sarmatians joined the Goths and other Germanic tribes (Vandals) in the settlement of the Western Roman Empire.