In the north of England improvements in the security of the Scottish border, and the rise of major noble families such as the Percies and the Nevilles, encouraged a surge in castle building at the end of the 14th century. Palace-fortresses such as Raby, Bolton and Warkworth Castle took the quadrangular castle styles of the south and combined them with exceptionally large key towers or keeps to form a distinctive northern style. Built by major noble houses these castles were typically even more opulent than those built by the nouveau riche of the south. They marked what historian Anthony Emery has described as a "second peak of castle building in England and Wales", after the Edwardian designs at the end of the 14th century.