Germania (Greek: Γερμανία) was the Greek and Roman geographic term for the geographical regions inhabited mainly by peoples considered to be Germani. It was most often used to refer especially to the east of the Rhine and north of the Danube. The areas west of the Rhine were mainly Celtic (specifically Gaulish) and had become part of the Roman Empire.
Some Germani, perhaps the original people to have been referred to by this name, had lived on the west side of the Rhine. At least as early as the 2nd century BC. This area was considered to be in "Gaul", and became part of the Roman empire. These were the so-called germani cisrhenani, who in modern terms lived in the region of modern eastern Belgium, the southeastern Netherlands, and stretching into Germany towards the Rhine. During the period of the Roman empire, more tribes were settled in areas of the empire near the Rhine, in territories controlled by the Roman Empire. Eventually these areas came to be known as Lesser Germania, while Greater Germania (Magna Germania; it is also referred to with names referring it being outside of Roman control: Germania libera, "Free Germany") was the larger territory east of the Rhine.
The Roman parts of Germania, "Lesser Germania", eventually formed two provinces of the empire, Germania Inferior, "Lower Germany", which came to eventually include the region of the original germani cisrhenani and Germania Superior, which in modern terms comprised an area of western Switzerland, the French Jura and Alsace regions, and southwestern Germany. Important cities were Besançon (Besontio), Strasbourg (Argentoratum), Wiesbaden (Aquae Mattiacae), and Mainz (Mogontiacum).
Read more about Germania: Origins of The Term, History, Roman Conquests, Modern Use