更新日：2024年2月27日

Hamamatsu Castle Stone Walls

Nozura-zumi (Natural Stacking of Stones)

Although the stone walls of Hamamatsu Castle look rough, unpolished, and perhaps ready to collapse at any time, they have withstood the harsh weather for over 400 years and still retain their original appearance.

These are some of the highest value cultural assets of the Hamamatsu Castle ruins.

The stone walls were made using nozura-ishi, or natural stones, that are placed on top of each other in a style called nozura-zumi, which uses the natural shape to forgo the use of mortar at the joints of the stones.

It is said that this style was commonly used until the Keicho period (1596 – 1615).

The levels of the walls are laid out going left-right on the horizontal axis, somewhat resembling the thread of a blanket, which brought about the name nuno-zumi (coursed masonry).

However, as the size and shape of the rocks are not uniform it causes the rocks on the horizontal axis to become dislodged, which is known as nuno-zumi collapse. Rather than just stacking irregularly-shaped stones, you stack the stones so that the large side of the stone faces upwards and the smaller side face downwards.

Gaps would be filled with irregularly-shaped smaller stones from the back of the wall to ensure that the bigger stones stay in place.

Cobblestones and gravel are then used to pack the back side of the wall.

The cobblestones are packed on about 1-1.5 meters and after all this is packed on, the wall can drain itself and resist collapse from built-up water pressure.

When looking at the stone wall from the front, small stones can be seen between the larger stones.

These are called ai-ishi (spacer rocks), and were used for shape but have no effect on the structural integrity of the wall.

It is said that these stone walls are strong enough that the spacer rocks can fall out without causing any structural issues.

The stone walls of Hamamatsu Castle, especially those around the keep foundation and castle gates, are very stable and make use of large rocks.

In addition, the stacking style is called sangi-zumi (which rectangular stones are arranged so the edges and sides alternate in the corners).

The slope of the stone wall is straight and has an incline of about 57 to 78 degrees.

Most of the stone material used in the walls is quartzite, but limestone and crystalline schist can also be found.

Quartzite can be found in the mountains to the northern shore of Lake Hamana, and the stones used in these walls were quarried in the present-day Ōkusayama and Nemotoyama mountains in the Shonai region or near Chibata in Kosai City on the opposite side of the lake.

It is presumed that the quarried stones were transported by boat to the eastern shore of Lake Sanaru and then brought to Hamamatsu Castle.

There is no accurate material to deduce the precise time frame in which these stone walls were built, however the prevailing theory is that they were built around the time when the second lord of Hamamatsu Castle, HORIO Yoshiharu, was in power (around 1590~).