in Japanese castles was the architecture. I was intrigued as to how a military structure could be strong and impenetrable, yet graceful and intricately detailed at the same time," says Mitchelhill.

"Consequently, the emphasis of our first book was on the architectural details. However, the individual stories behind each castle still needed to be told: "How they came to be, why they are situated where they are, and why a particular lord built the castle, yet did not stay there very long."

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What's important to understand about the samurai?

"The samurai were warriors. The period in which the castles in this book were built spanned the end of the Warring States period in the late 16th century until the earlyyears of the Tokugawa Shogunate or Edo era (1600-1868)," says Mitchelhill.

"This era was a feudal period with a strict class system. The Shogun was the supreme military leader, the daimyo was lord of a region, and the samurai were the daimyo's retainers or army.

"But the samurai were not just warriors. They were also castle-builders, politicians and local leaders with a great aesthetic sense."

How many castles are there in total in Japan?

Mitchelhill's book documents 24 Samurai-era castles, including Iyo-Matsuyama, on Shikoku island, pictured here. David Green

"The number of castles has varied greatly over the past 500 years," says Mitchelhill. "During the Warring States period in the 15th and early 16th centuries, thousands of fortifications were built to protect a warrior's territory."

"Toward the end of this period as Japan was