Before becoming Normandy, this fertile region was home to Celtic tribes until Roman legions arrived in 50 BC. The Romans called it Gallia Lugdunensis and built the city of Rouen which is the capital of Normandy today. Christianity arrived in the 3rd century, with monasteries emerging across the landscape. After Rome's fall in the 5th century, the region fell under Frankish control. You can still see traces of this ancient past in places like Lillebonne's Roman theater and Rouen's archaeological museum.