The first Emperor of Japan ascended the throne perhaps 1,600 years ago, and after his direct descendent, the present Emperor, inherited the office 12 years ago, he donated 6,000 heirlooms to the nation. Nearly 200 are being exhibited together for the first time at the Heiseikan galleries in Ueno.

Approaching the bright new building past a bubbling stream prepares us for something special. "Treasures of the Imperial Collections" lives up to its name; here is some of the finest art in Japan. Exhibits range from tomb relics of the Yayoi Period to oil paintings of the 20th century, yet this rich diversity shows a remarkable continuity of tradition.

Throughout the centuries, waves of foreign influence have washed up on these shores. Each has made its mark, but Japanese artistry is still unique, and it is fascinating to trace motifs and sensibilities through the ages. For example, the bronze dotaku bells of purely Japanese design have been silent for perhaps 2,000 years, and we can only conjecture about their ritual use. But the patina reveals an abstract design of flowing water, appropriate for an island nation and rites of purification. Such stylized waves appear many times in the exhibits, as they still do on many everyday textiles, pottery and paper.

The legendary 7th century regent Prince Shotoku has been called the Prince Charming of Japanese history, but a scroll of his calligraphy reminds us of his real, civilizing role in society. Writing was adopted from China around the 5th century, and by the 9th century in the Heian Period, a distinctive, flowing Japanese style had developed. Turning an elegant phrase and writing in a beautiful hand were two essential accomplishments in courtly life, and reputations could be won or lost at a poetry contest or exchange of letters.

It is quite thrilling to see diaries and poems written by contemporaries of Murasaki Shikibu and Sei Shonagon, Heian court ladies who wrote the classic "Tale of Genji" and "Pillow Book," respectively. (A few English translations would be very welcome, though.)

The fine calligraphy also reveals Japan's early talent for producing exquisite paper, and in exhibit 69 (poems by Fujiwara no Yukinari) the silvery background design of the seashore is pleasingly familiar too. It is wonderful that documents such as a poet's 12th-century copy of the "Sarashina Diary" have survived fires, wars and moths, and their preservation is a mark of the great respect accorded to the twin arts of poetry and calligraphy.

After all this elegance the flying arrows of the "Mongol Invasion Scroll" brings history even more vividly to life. Then the gallery of Edo art explodes in a wall-to-wall array of bird-and-flower paintings: 13 scrolls by Ito Jakuchu (1716-1800) from a series originally owned by the Shokoku-ji Temple. The artist took 10 years to paint 30 of these delightful scrolls, but when the temple fell on hard times they were donated to Emperor Meiji in exchange for a grant. The "Colorful Realm of Living Beings" shows the exuberant side of Japanese art, produced in a period of cultural isolation when earlier European influence was quietly absorbed into something very Japanese. Close up, one can see each frond or feather has been painted separately. Stand back and one can appreciate the composition and control of color. In the "Group of Roosters" the artist has captured the strutting birds so well one can almost hear them squawk, and the red coxcombs send the eye on a happy dance through the riot of feathers.

After all these fireworks one turns to Hokusai's simple painting of a watermelon with a sweet feeling of coolness. It is a lovely rendition of transparency, and the smooth roundness of the melon contrasts with the flat knife and crinkled parings. One can imagine the painter intrigued by this challenge, but it is not an academic exercise. Hokusai always seems immersed in his subjects, and can combine delicacy with panache.

Nature, literature and romance combine in Maruyama Ookyo's courtly screen painting of Prince Genji's mansion in the four seasons. There is both realistic treatment in details such as the maple leaves, and abstract treatment in the ripples of water that melt into a golden mist. After so many centuries of East Asian sensibility it is quite a shock to see portraits of Emperor Meiji and Empress Shoken in the realistic Western manner. It gives us some idea of the impact of Western art in the 1870s, when the era of isolation came to an end. The role of art in daily life began to change, and government ministers, eager to market Japan to the West, urged artists to exhibit in various world fairs.

The vase by Yasuyuki Namikawa was exhibited in 1899, and must have been greatly admired for its beautiful blossoms and birds. Yet one has mixed feelings about this and the metal figures of the bugaku dancers. The artists' skill almost surpasses belief, but these are strange hybrids of East and West. Their sense is quite different from an album of poetry to be read on an autumn night, or a lacquer writing box opened to reveal golden fireflies.

Still, they are important as they show the country in its headlong rush into modernity, with all its pleasures and perils. So in the final section it is satisfying to see 20th-century artists such as Taikan Yokoyama returning to the mystery of the seasons, and the eternal power of Mount Fuji and its inky foothills.

As one leaves the galleries, the ancient bronze bells echo once again, this time through the wave-patterned tiles of the brand-new hall.