With their thick walls and iron-clad windows, most of the world’s beautiful castles were originally built to keep enemies at bay and to house and protect royal rulers and members of the nobility. Medieval warfare was a thing of the past, though, when beautiful castles started to appear in America. These extravagant structures were built not as fortresses or royal residences but as temples to wealth and power—often by American royalty, including business magnates such as publisher William Randolph Hearst, railroad baron Jay Gould, and the members of the Vanderbilt family. Today, some are located far from civilization, while others are in the middle of cities. They range from stately manors to grand civic buildings. Castles in the US may not have as long a history as the beautiful castles of Europe, but their stories can be just as fascinating. Here, AD rounds up 18 of the most beautiful castles across the country.