If a road or a city that ends (and/or starts) on a castle tile is completed, all players with a majority of followers on the completed road or city score(s) 3 bonus points per involved castle.[1][2] It does not matter whether the castles are occupied or not.
↑ Thus, a road that had each end on a different castle tile would score 6 bonus points. A road that began and ended on the same castle tile would receive 3 bonus points. (4/2015)
↑ These bonus points are added to the feature score after modifications from inns or cathedrals. (10/2015)
Thus, a road that had each end on a different castle tile would score 6 bonus points. A road that began and ended on the same castle tile would receive 3 bonus points. (4/2015)
These bonus points are added to the feature score after modifications from inns or cathedrals. (10/2015)