Baronial castles were of varying size and sophistication; some were classed as a "caput", or the key stronghold of a given lord, and were usually larger and better fortified than the norm and usually held the local baronial honorial courts. The king continued to exercise the right to occupy and use any castle in the kingdom in response to external threats, in those cases he would staff the occupied castles with his own men; the king also retained the right to authorise the construction of new castles through the issuing of licenses to crenellate. It was possible for bishops to build or control castles, such as the important Devizes Castle linked to the Bishop of Salisbury, although this practice was challenged on occasion. In the 12th century the practice of castle-guards emerged in England and Wales, under which lands were assigned to local lords on condition that the recipient provided a certain number of knights or sergeants for the defence of a named castle. In some cases, such as at Dover, this arrangement became quite sophisticated with particular castle towers being named after particular families owing castle-guard duty.