the veracity of this account has been clouded by later fictional publications depicting Saizō as one of the legendary Sanada Ten Braves. Uesugi Kenshin, the famous daimyō of Echigo Province, was rumored to have been killed by a ninja. The legend credits his death to an assassin who is said to have hidden in Kenshin's lavatory, and fatally injured Kenshin by thrusting a blade or spear into his anus. While historical records showed that Kenshin suffered abdominal problems, modern historians have generally attributed his death to stomach cancer, esophageal cancer, or cerebrovascular disease. Psychological warfare In battle, the ninja were also used to cause confusion amongst the enemy. A degree of psychological warfare in the capturing of enemy banners can be seen illustrated in the Ōu Eikei Gunki, composed between the 16th and 17th centuries: Countermeasures A variety of countermeasures were taken to prevent the activities of the ninja. Precautions were often taken against assassinations, such as weapons concealed in the lavatory, or under a removable floorboard. Buildings were constructed with traps and trip wires attached to alarm bells. Japanese castles were designed to be difficult to navigate, with winding routes leading to the inner compound. Blind spots and holes in walls provided constant surveillance of these labyrinthine paths, as exemplified in Himeji Castle. Nijō Castle in Kyoto is constructed with long "nightingale" floors, which rested on metal hinges (uguisu-bari) specifically designed to squeak loudly when walked over. Grounds covered with gravel also provided early notice of unwanted intruders, and segregated buildings allowed fires to be better contained. Training The skills required of the ninja have come to be known in modern times as , but it is unlikely they were previously named under a single discipline, rather distributed among a variety of espionage and survival skills. Some view ninjutsu as evidence that ninja were not simple mercenaries because texts contained not only information on combat training, but also information about daily needs, which even included mining techniques. The guidance provided for daily work also included elements that enable the ninja to understand the martial qualities of even the most menial task. These factors show how the ninjutsu established among the ninja class the fundamental principle of adaptation. The first specialized training began in the mid-15th century, when certain samurai families started to focus on covert warfare, including espionage and assassination. Like the samurai, ninja were born into the profession,