The term 'Royal Palace' can be summed up by the crossword solution of 'CASTLE'. A CASTLE is a large fortified structure, typically built in Europe and the Middle East during the Middle Ages by nobility or royalty to control the area immediately surrounding it. Castles were often used as defensive structures and residences for the ruling family. Royal Palaces are a type of CASTLE that were used as the official residence of a monarch or other royal figure.