Samurai Castle

Samurai castle takes a look at famous Japanese Kumamoto castle, built in the 17th century, and its reconstruction after an earthquake in 2016.

A recent earthquake (April 2016) reveals ancient engineered stone walls withstood the natural disaster, while all newer walls collapsed (post Meiji era).

Why were the old walls able to withstand it? Did the old samurai engineers know something we do not?

NHK (documentary production crew) investigates with a series of engineering and historical expert interviews, drone shots creating 3D models and examine the math behind 17th century samurai engineers.

When construction originally started on the Kumamoto castle in the end of the 16th century, Japan saw frequent earthquakes.

To solve this, samurai masters devised many technical innovations to prevent and prepare for these natural disasters.

Kumamoto castle's sloping stone wall math equation
Kumamoto castle’s sloping stone wall math equation

One of these innovations was a math equation which astounds experts of today.

The math behind it is easily seen on Kumamoto castle in its curving stone walls called musha-gaeshi (samurai proof).

Stone walls stacked parallel to the ground has a tendency to break loose, when sideways forces are exerted by an earthquake. If the stones are sloped at a 90 degree sloping angle – the forces disperse more evenly causing less damage.

The 17th century Japanese engineers knew this and created a formula to build more solid constructions through the musha-gaeshi.

Join in as NHK leads us deeper into the history behind Kumamoto castle to unveil more mysteries.

Samurai Castle
  • Info
  • Release date2016
  • Full runtime
  • Director(s)Shota Tsuchida, Hirofumi Abe
  • Production companyNHK