An oppidum (plural oppida) is a large fortified Iron Age settlement. Oppida are associated with the Celtic late La Tène culture, emerging during the 2nd and 1st centuries BC, spread across Europe, stretching from Britain and Iberia in the west to the edge of the Hungarian plain in the east. They continued in use until the Romans began conquering Europe. North of the River Danube, where the population remained independent from Rome, oppida continued to be used into the 1st century AD.