Koreans continued to harbor a defiant attitude towards the Qing dynasty in private while they officially yielded obedience and sentiments of Manchu barbarity continued to pervade Korean discourse. Joseon scholars secretly used Ming era names even after that dynasty's collapse and many thought that Joseon should have been the legitimate successor of the Ming dynasty and Chinese civilization instead of the "barbaric" Qing. Despite the peace treaty forbidding construction of castles, castles were erected around Seoul and northern region. Hyojong of Joseon lived as a hostage for seven years in Mukden until he succeeded Injo. Hyojong planned an invasion of Qing called Bukbeol (북벌, 北伐, Northern expedition) during his ten years on the Joseon throne, though the plan died with his death on the eve of the expedition.