A List of American castles. Every famous castle from United States has been included, with photos. This USA castles list is in alphabetical order by the name of the castle. Originally made of earth and wood, later castles were built of stone, including the majority of these American castles, so many still survive today. Spanning a period of 900 years during the middle ages, castles come in many styles of architecture and design. Despite their differences though, they all have one feature in common-- they are fortified. Castles are defensive structures specifically built to withstand attack in the medieval world. Technologies such as arrowslits, murder-holes, and moats further improved their capabilities. Castles finally fell out of favor with the advent of gun powder, as offensive technologies, such as canons, rendered castles largely obsolete. Of course, American history does not go back to the medieval days, so the majority of these castles were built more for show than for any defensive security reasons. Castle builders are an eccentric lot to be sure.