Complex sentence: The Pre-Roman Iron Age (5th/4th century BC-1st century BC) designates the earliest part of the Iron Age in Scandinavia, northern Germany, and the Netherlands north of the Rhine River, i.e. the first of three periods in Oscar Montelius's chronology system.
Split into simpler sentences: The Pre-Roman Iron Age (5th/4th century BC-1st century BC) designates the earliest part of the Iron Age in Scandinavia, northern Germany, and the Netherlands north of the Rhine River. It is the first of three periods in Oscar Montelius's chronology system.