The first feudal lord Maeda Toshiie started building the castle almost as soon as he entered it. First he constructed the donjon, the main watchtower. Reportedly, he invited Takayama Ukon, who was well known as a Christian lord at that time, to learn how to build a great castle. The donjon looked very dignified. It was the most important symbol of the castle and was located at the center of Hon-maru. There is no record regarding when its construction was finished. On October 30th, 1602, lightning started a large fire, which quickly spread to the powder house. As a result, almost all the buildings at Hon-maru were destroyed.