What did people built as strong fortresses for protection?

People built strong fortresses, often called castles, as protective structures against invasions and attacks. These fortresses were typically constructed from durable materials like stone and featured thick walls, moats, and towers for defense. They served not only as military strongholds but also as residences for nobility, providing safety for those within during times of conflict. Additionally, many fortresses were strategically located on elevated ground or near vital resources to enhance their defensive capabilities.