Umiiso Mirror (donated by Empress Mei of Nikko in February

Two Tang-Style Mirrors Empress Kōmyō Gave in 736

The Kaikikyō, or "sea-and-shore mirrors," are a matched pair of large bronze mirrors held at the Tokyo National Museum. Each measures roughly 46 centimeters across, which places them among the biggest ancient mirrors to survive in Japan. They take their name from a single phrase in an eighth-century temple inventory, where the scene on their backs is described as a view of sea and rocky coast.

Their early history is recorded with unusual precision. The Hōryūji Garan Engi narabini Ruki Shizaichō, an asset register compiled at Hōryūji in 747, states that Empress Kōmyō presented two mirrors to the temple on the twenty-second day of the second month of Tenpyō 8, the year 736. That date marked the death anniversary of Prince Shōtoku, the statesman traditionally credited with founding Hōryūji, so the gift belongs to the earliest layer of devotion to his memory.

The register even notes the diameters of the two pieces. Converted from the small Tang measure used in the document, those figures fall close to the actual sizes of the surviving pair. That match is part of why scholars connect these mirrors with the eighth-century donation rather than with later replacements.

Why the Pair Was Named a National Treasure

The mirrors were classed as an Important Cultural Property in 1957 and raised to National Treasure status in 1964. Their value rests on three points at once: their size, the quality of the casting, and a provenance that can be traced back more than twelve centuries.

They were cast in white bronze, an alloy with a higher tin content than ordinary bronze. The extra tin makes the metal harder and gives a polished face a pale, silvery sheen. Gamma-ray radiography carried out by the museum found that the molten metal had flowed cleanly into the mold, which confirmed the skill behind the work. A 1980 fluorescence analysis of one mirror put its tin content near 45 percent, with copper making up most of the rest.

Where the mirrors were made is still argued. The Agency for Cultural Affairs records them as Tang Chinese work. Other specialists read the style as eighth-century and raise the possibility that they were cast in Japan after Chinese models, a class of object known as bōseikyō. The two readings agree that the imagery follows continental taste, and the question of origin stays open.

Reading the Landscape on the Back

Turn a mirror over and the reverse becomes a small relief landscape. A hemispherical knob sits at the center, pierced for a cord. From the four directions, triangular peaks rise toward it, and the spaces between are filled with curling waves.

Look closer and the scene fills with life. Birds rest on the water, figures fish from small boats, and one person seems to ride a piece of driftwood. On the islands and slopes stand deer in male and female pairs, lions, long-tailed birds, and scattered trees. Taken together, the elements point to a Daoist vision of sacred mountains and the immortals said to live among them, an idealized world of peace and plenty.

The name calls the setting a sea, yet the waterbirds are mandarin ducks, which favor rivers and lakes. That small disagreement has led some to suggest the scene shows fresh water rather than open ocean.

The two mirrors repay a side-by-side look. Their designs match almost line for line, differing mainly in the ripples around the central knob. It has never been settled if a single mold served for both, and comparing them in the gallery is the closest a visitor comes to that question.

Visiting the Gallery of Hōryūji Treasures

The mirrors belong to the Hōryūji Treasures, a group of more than three hundred objects that Hōryūji gave to the Imperial Household in 1878, when the temple faced severe financial strain. The collection later passed to the Tokyo National Museum, where it is often ranked alongside the Shōsōin repository in Nara as a record of early Japanese art.

These objects have their own building inside the museum grounds at Ueno Park. The Gallery of Hōryūji Treasures, designed by the architect Yoshio Taniguchi and opened in 1999, is a quiet, restrained space set back from the busier halls. The metalwork room on the upper floor is where the mirrors and related bronzes appear.

Because the collection rotates and individual pieces rest between showings, anyone hoping to see the Kaikikyō should check the museum's current exhibition listing before a visit. The museum stands a short walk from Ueno Station and shares the park with several other major museums, so a combined day of viewing is easy to plan.