Sheffield, provincial capital of South Yorkshire, is a low-rise city built around the steel industry. The first remnant of a settlement in Sheffield dates back to an Iron Age fort, probably built by the British tribe of Brigantes to defend against the Romans. A castle was built around 1150 at the confluence of the rivers Don and Sheaf, and the town grew around it. Sheffield played an important role in the industrial revolution, as both Crucible steel and Sheffield Plate were invented here, and the city continues to be one of the world's most renowned steel cities. Height restrictions are in place across most of the city centre to protect views of Sheffield Town Hall and the two cathedrals, so there are few high-rise buildings. The majority are residential tower blocks, built in the 1960s by the local council, but many are now being torn down to make way for less imposing structures. One of the few to survive is also the best and one of Europe's largest protected buildings, Park Hill Flats .