Castles in Scotland emerged as a consequence of the centralising of royal authority in the 12th century. Prior to the 1120s there is very little evidence of castles having existed in Scotland, which had remained less politically centralised than in England with the north still ruled by the kings of Norway. David I of Scotland spent time at the court of Henry I in the south, until he became the Earl of Huntingdon, and returned to Scotland with the intention of extending royal power across the country and modernising Scotland's military technology, including the introduction of castles. The Scottish king encouraged Norman and French nobles to settle in Scotland, introducing a feudal mode of landholding and the use of castles as a way of controlling the contested lowlands. The quasi-independent polity of Galloway, which had resisted the rule of David and his predecessors, was a particular focus for this colonisation. The size of these Scottish castles, primarily wooden motte-and-bailey constructions, varied considerably from larger designs, such as the Bass of Inverurie, to smaller castles like Balmaclellan. As historian Lise Hull has suggested, the creation of castles in Scotland was "less to do with conquest" and more to do with "establishing a governing system".