The depiction of ninjas carrying swords on their backs, specifically in the form of a long sword or katana, is primarily a product of modern popular culture, including movies, novels, and video games. In historical context, there is limited evidence to support the notion that ninjas commonly carried swords on their backs.

Ninjas, also known as shinobi, were covert agents and practitioners of unconventional warfare in feudal Japan. They were known for their skills in espionage, sabotage, guerrilla tactics, and intelligence gathering. Their approach to warfare often involved stealth, deception, and using the environment to their advantage.

Ninjas were adept at adapting to their circumstances and would utilize a variety of weapons based on their missions and specific needs. While swords were among the weapons they employed, they would typically choose smaller and more concealable blades, such as the tanto (dagger) or the ninjato (a fictionalized short sword associated with ninjas in popular culture).

The portrayal of ninjas carrying large swords on their backs is largely a creative interpretation and artistic license found in modern media. This depiction has contributed to the romanticized image of the ninja as mysterious, highly skilled warriors. However, it does not accurately reflect historical ninja practices or the weapons they typically used.

Ninjas would often conceal their weapons to maintain their stealth and surprise advantage. They might carry small blades on their person or hide weapons within their clothing, tools, or other inconspicuous objects.

It's important to approach the subject of ninjas with a critical eye, separating historical reality from fictionalized portrayals. While ninjas were skilled and resourceful warriors, their methods and equipment were diverse and adaptable, and they did not conform to a single, universally recognized image or set of practices.