says Mitchelhill. "Two of the most well-known castle designers were the daimyo Todo Takatora and Kato Kiyomasa."

"Todo Takatora is said to have designed about 20 castles, the largest and most important being Edo castle.

"Other castles by Todo were Wakayama, Uwajima, Imabari, Iga Ueno and Sasayama."

"Kato Kiyomasa designed Kumamoto and Nagoya castle. He was known for his skill at building sheer stone walls. There is a huge stone in one of the walls at Nagoya castle dedicated to him called the Kiyomasa stone."

What did you find surprising when documenting the architecture?

"Even though samurai castles are architecturally similar in terms of stone walls, moats and timber towers, they differ vastly in size, layout and specific aesthetic features," says Mitchelhill.

"Each castle had to be unique for defensive purposes in order toconfuse an invading enemy. In addition, the enormous castles were built in just a couple of years using local manual labor.

"On the orders of the daimyo, peasants built stone walls of up to 30 meters high (98 feet), dug moats up to eight meters (26 feet) deep, transported huge boulders to be placed at important entrance ways, and constructed countless timber, mud and plaster buildings."

Which castles have the most interesting defensive strategies?

"Nagoya, Osaka and Kumamoto castles all have massive sheer stone walls which curve inwards.

"The stones in these walls are fit tightly together to eliminate footholds for intruders seeking to scale them," explains Mitchelhill.

"Osaka's walls rising from the moats resemble an open fan, with each crease or corner protected by a tower. Castle defenders could shoot at invaders