Germania Inferior ("Lower Germania") was a Roman province from AD 85 until the province was renamed Germania Secunda in the 4th century AD, on the west bank of the Rhine bordering the North Sea. The capital of the province was Colonia Claudia Ara Agrippinensium (modern-day Cologne).
According to Ptolemy (2.9), Germania Inferior included the Rhine from its mouth up to the mouth of the Obringa, a river identified with either the Aar or the Moselle. The territory included modern-day Luxembourg, the southern Netherlands, part of Belgium, and part of North Rhine-Westphalia in Germany, west of the Rhine.
The principal settlements of the province were Castra Vetera and Colonia Ulpia Traiana (both near Xanten), Coriovallum (Heerlen), Albaniana (Alphen aan den Rijn), Lugdunum Batavorum (Katwijk), Forum Hadriani (Voorburg), Ulpia Noviomagus Batavorum (Nijmegen), Traiectum (Utrecht), Atuatuca Tungrorum (Tongeren), Bona (Bonn), and Colonia Agrippinensis (Cologne), the capital of Germania Inferior.
Germani cisrhenani
The first confrontations between a Roman army and the peoples of Germania Inferior occurred during Julius Caesar's Gallic Wars. Caesar invaded the region in 57 BC and in the next three years annihilated several tribes, including the Eburones and the Menapii, whom Caesar called "Germanic" but who probably were Celtic or at least mixed Celtic-Germanic. Germanic influence (mainly through the Tungri) increased during Roman times, leading to the assimilation of all Celtic peoples in the area. In fact, Germania Inferior had Roman settlements since around 50 BC and was at first part of Gallia Belgica.
It was only under Domitian (r. AD 81–96) that new territories were acquired, between the high valleys of the Rhine and the Danube, following the campaigns conducted by his generals in AD 83–85, which led to the creation of two new imperial provinces, lower and upper Germany. Although this region had been occupied since the reign of Augustus, it wasn't formally established as a Roman province until around AD 85, with its capital at Colonia Claudia Ara Agrippinensium (modern-day Cologne).