Dear Alice,
Is it weird to love a wall? I recently visited the Imperial Palace in Tokyo and was totally blown away by a high rock embankment on the far side of the moat. That rugged face! Those elegant lines! I am completely enchanted and want to know anything at all you can tell me. But there's one thing that bothers me: Aren't walls like that built for defense? If so, why the heck didn't they make it smoother and steeper? With all those spaces between the rocks it would be a cinch to climb.

Lucy P., Ibaraki Prefecture

Dear Lucy,
The wall that wowed you is what's called ishigaki in Japanese. These beautiful stone constructions are seen all over Japan but are most strongly associated with castles. (The Imperial Palace stands on the site of what used to be Edo Castle, and the stone walls were part of the original castle stronghold.)

Building an ishigaki is an enormous undertaking involving sophisticated engineering, endless labor and a "dry" construction method, which means no mortar is used. I knew that much, but to fill in the chinks I took your question to Yasuhiro Nishigaya, an expert on Japanese castles and the author of dozens of books on the subject.

You'll be relieved to know he wasn't the least bit surprised that you're smitten.

"A few years back I did a series of 24 magazine-type books, each on an individual castle," Nishigaya told me. "The publisher put in reader-reply cards asking buyers what they liked about castles, and a full 60 percent of respondents said 'ishigaki.' There is something about these structures that really speaks to people."

The wall you saw at the Imperial Palace dates back about 400 years, and has withstood fire, war and natural disasters. In 1604, the Tokugawa Shogunate announced plans to build a huge castle at Edo, and since stone was scarce near the building site, ordered a number of territorial lords not only to provide stone for the project, but also to build the fortifications. In effect, the shogun was killing two birds with one stone — getting his castle built for him while keeping potential rivals busy and bankrupt.

You can tell where the stones came from by their color: the black rock came from Ito on the Izu Peninsula; the reddish rock came from Nebukawa, in roughly the same region, while the white rock was hauled all the way from the Inland Sea. Getting stones from Izu to Edo was a massive undertaking as the larger blocks weighed up to several tons each and required 100 men to move. They were carried by sea to Edo on special transport vessels, and then dragged on sledges to the building site.

The first step in constructing ishigaki is to prepare the supporting earth embankment, cutting narrow terraces into in a steplike pattern. Workers then put down a thick layer of small river stones,arranging elaborate paths for rainwater runoff. With Japan subject to torrential rainfalls, the danger is that water pressure will build up inside the wall during heavy rain and cause it to collapse if adequate drainage isn't provided.

It was only after this laborious groundwork that workers could lay the rocks you see from the outside, carefully fitting them to create a strong and visually attractive structure. You see many different styles of stone work in ishigaki, ranging from loose patterns that use the stones in pretty much their natural state to highly refined patterns of carefully cut and processed stones. In general, the stones on early walls are less worked than those used in later constructions.

I'd always wondered why you don't see mortar in Japanese stone walls, so I asked Nishigaya about that. Although Japan did have the bonding technology necessary to make mortar, he said, a wall constructed by mortaring stones together would be fixed and non-porous, and therefore totally unsuitable in a country with earthquakes and heavy rainfall.

The prevalence of earthquakes in Japan had a strong influence on ishigaki design. In 1596, a massive earthquake hit the area around Kyoto, completely destroying Fushimi Castle. That loss led to reforms in castle design, including building the walls with a more moderate incline to disperse the force of gravity across a wider area. Of course it was just that gentle slope that led you to comment on how easy it would be to scale a Japanese castle wall, but Nishigaya dismissed it as being a real issue for defense.

"The last thing you want, when you design a castle, is to make it appear impregnable," he cautioned. "If you do, your enemies will be discouraged from attacking and opt for a siege instead. No one wants to be surrounded and cut off from supplies and reinforcements. So you invite your enemy to attack by creating spots that seem vulnerable, and develop your defenses knowing exactly where you're likely to be hit."

Appreciating your appreciation, Nishigaya volunteered another admirable point about castle walls in Japan.

"Did you notice how they are square, with distinct corners? This is very different from Europe and China, where castle walls were rounded because it's much more difficult to construct a square wall," he observed. "This technology was developed in Japan long before it appeared in other countries."

The corner stones support the wall, so the size and number of corner stones is carefully determined to suit the height of the entire structure.

In case you want to test your love by seeing a few more walls, I asked Nishigaya for a list of his favorites. He offered three: The ishigaki at Kumamoto Castle, built in 1620 of an unusual volcanic rock, because they are particularly steep and technologically advanced; the walls at Osaka Castle, constructed in the same year, because at 32 meters they are the tallest in Japan; and Edo Castle, because, being earlier than the other two, "you can see the technology in its earlier stage, before wall-building reached its zenith."

For more information in English, take a look at Akira Naito's illustrated history "Edo, the City That Became Tokyo" (Kodansha International, 2003). The book has several sections with helpful drawings explaining what went into the building of the stone walls of Edo Castle. And it's a fun, easy read in general. Puzzled by something you've seen? Send a description, or better yet a photo, with the address where you saw it to [email protected] or Alice Gordenker, A&E Dept., The Japan Times, 4-5-4 Shibaura, Minato-ku, Tokyo 108-8071