Nam Giao Esplanade

South of the Hue Citadel, in the dark of night, the emperor stepped out of Trai Cung and walked toward the altar of Heaven. It was only two in the morning. He wore a dragon robe and a ceremonial headdress, and he held a jade tablet in both hands. Ahead of him rose a round terrace, topped by a blue tent called Thanh Ốc. Bells, drums and stone chimes began to sound.

That was a night of the Tế Giao rite at the Nam Giao Esplanade. Here the emperors of the Nguyễn dynasty made offerings to Heaven and Earth. The Nguyễn dynasty was Vietnam's last royal dynasty, which reigned from 1802 to 1945.

Work on the altar began on March 25, 1806, under Emperor Gia Long, the founder of the Nguyễn dynasty. The first ceremony took place on March 27, 1807. Today it is the only altar to Heaven left in Vietnam.

That night did not begin at two in the morning. It began long before.

The court's Bureau of Astronomy had to choose an auspicious day. The Ministry of Rites and the Ministry of Works spent months on the preparations. The emperor kept himself pure for three days. He ate vegetarian food and calmed his mind. He issued an edict thanking his officials and reducing the sentences of prisoners.

Then came the morning of departure. At eight in the morning, the emperor left the Imperial City in a royal palanquin. The procession was split into three parts, a front, a middle and a rear section. Two elephants led the way, followed by officials on horseback carrying flags. There were flags of the five elements: metal, wood, water, fire and earth. There were flags of the four directions, showing the Azure Dragon, the White Tiger, the Vermilion Bird and the Black Tortoise. There was even a parasol embroidered with nine dragons.

In the years before Trường Tiền Bridge was built, the whole procession crossed the Perfume River on a pontoon bridge made of boats. On the far bank, it followed the roads now named Phan Bội Châu and Điện Biên Phủ. Along the way, people built welcome gates and set out incense tables on both sides of the road.

At Nam Giao, the emperor went to rest in Trai Cung, the Fasting Palace, at the southwest corner of the altar. Here he kept his heart pure through the last night before the rite.

The courtyard of the Fasting Palace also holds a story about trees. Emperor Minh Mạng planted 10 pine trees here with his own hands. The princes planted pines along the road the emperor traveled. Officials of the fourth rank and above were allowed to plant a pine as a keepsake. Each tree had a plaque of bronze or stone bearing the planter's name and title. So the pine forest slowly grew around the altar.

An emperor traveled far, stayed awake through the night and kept himself pure, all for an offering to Heaven. There was a reason for it.

In the old way of thinking, the emperor was the Thiên tử, the Son of Heaven. The Tế Giao rite was his moment to show reverence to Heaven and Earth and to the spirits. It was also a moment to remind himself to govern well, so the people could live in peace, and the rains and winds would come in their season.

And the shape of the altar itself tells how people of old saw the universe.

The altar has three tiers. The lowest tier is square, with railings limewashed red. It stands for humankind. The middle tier is Phương Đàn, also square, with railings limewashed yellow. It stands for Earth. On top of Phương Đàn, a yellow tent called Hoàng Ốc was raised.

The highest tier is Viên Đàn, the round altar, with railings limewashed blue. It stands for Heaven. Viên Đàn is 40.5 meters across and 2.8 meters high. Around its surface lie 28 stone blocks with holes cut into them. They held the poles of the blue tent, Thanh Ốc.

Heaven is round, and the earth is square. People below, earth in the middle, Heaven above. To climb step by step from the red tier to the yellow tier and then to the blue one is to travel from the ground up to the sky.

Now, back to the night of the rite, at two in the morning.

The ritual music had nine pieces, sung at nine different stages of the ceremony. 128 dancers performed the Bát Dật dance. Gongs, drums, horns, two-string fiddles and flutes blended together in the deep of the night. The offerings were a buffalo, a goat and a pig, fattened beforehand on clean feed. In the southeast corner stood a furnace, where the sacrificial animal was burned as an offering to Heaven.

The whole ceremony lasted nearly three hours. Then the procession formed up again and headed home. When the emperor reached Đại Cung Môn, the Great Palace Gate, the gunners fired nine shots in celebration. Only then was that year's Tế Giao rite truly over.

In the early years of the Nguyễn dynasty, the rite was held once a year, in the second lunar month, as spring was arriving. In 1890, under Emperor Thành Thái, the court changed the rule. From then on, the rite was held only once every three years. It fell in the years of the Rat, the Cat, the Horse and the Rooster.

The altar served for 138 years, from 1807 to 1945. In that time it saw 98 great offerings to Heaven, under 10 Nguyễn emperors. The line began with Gia Long and Minh Mạng. Later came Thiệu Trị and Tự Đức. The last was Bảo Đại.

The last rite took place before dawn on March 23, 1945, under Emperor Bảo Đại. A few months later, the Nguyễn dynasty came to an end. The ritual music at Nam Giao fell silent for many years.

Almost 60 years later, in 2004, the Tế Giao rite was revived for the first time during the Hue Festival. In the festival seasons that followed, the procession again set out from Ngọ Môn, the Noon Gate. Elephants, horses, flags and parasols moved one after another toward the south.

On December 11, 1993, UNESCO recognized the Nam Giao Esplanade as World Cultural Heritage, as part of the Complex of Hue Monuments. The grounds of the altar stretch 390 meters, ringed by a forest of old pines.

If you stand at the foot of Viên Đàn today and look up, there is no blue tent anymore, and no ritual music. There is only a round patch of sky, just as people of old imagined it.

And all around, the wind still moves through the pine forest, where an emperor, princes and officials once planted trees with their own hands. The pine crowns rustle softly, as if the nine pieces of ritual music from long ago were still playing, far away.