Ha Long Bay

340 million years.

That is how much time has passed since the first layers of limestone began to build up on the floor of a shallow ancient sea, in the place that is now Ha Long Bay. Since then, the land has risen and sunk again, and the sea has come in and drawn back. Over 20 million years, rain and groundwater hollowed out the rock from within. Then, about 10,000 to 15,000 years ago, after the last ice age, the sea rose. It flooded the feet of the stone mountains that had already formed, and it closed in around their tall peaks. The result was a landscape that few other places in the world can match.

The work of those 340 million years is nearly 2,000 islands, most of them limestone, standing straight up out of a blue-green sea. To be exact, there are 1,969 of them.

This is Ha Long Bay, a UNESCO World Natural Heritage Site that has been inscribed twice. The first time, in 1994, was for its exceptional beauty. The second time, in 2000, was for its geology and the shape of its land. UNESCO uses a technical phrase to describe this place: "the most extensive and best-known example of marine-invaded tower karst in the world." In everyday words, nowhere on Earth are limestone mountains standing in the sea more extensive or better known than here.

In 2023, UNESCO extended the site to take in the Cát Bà Archipelago of Hải Phòng. The whole heritage area now covers more than 656 square kilometers.

The islands here are steep, with sharp peaks. They do not slope gently down like ordinary hills, because they are made of limestone. Rain and seawater eat into limestone from the outside in. Where the rock is hard, it stays. Where it is weaker, it wears away. What remains are strange, sharp shapes, and no two places look alike. Each island is a work of its own, made by time and water.

Inside many of the islands are caves. Some were dug through the rock from within by groundwater, over millions of years. Some were worn out of the foot of an island by rain and waves. Others formed where the waves pounded straight into the cliff face. Each way of forming leaves its own shape and mood, so every cave is unlike the others.

Sửng Sốt Cave, on Bồ Hòn Island, is one of the largest and best known. It covers about 10,000 square meters and runs about 200 meters long. It is divided into two chambers, and the ceiling of the first one rises as high as 30 meters. As a boat draws near, the mouth of the cave looks small and low, nothing special at all. But once inside, the space suddenly opens wide. That is when the name Sửng Sốt, which means astonished, begins to make sense.

Thiên Cung Grotto, on Đầu Gỗ Island, also covers about 10,000 square meters. But it sits higher up, 25 meters above the sea. Inside, its stalactites and dripstone shine in many colors under the lamps. And Luồn Cave, on Bồ Hòn Island, has an arch only about 3 meters high, right at the surface of the water. It leaves just enough room for small bamboo boats to slip through.

From a boat in the middle of the bay, the cliffs rise on every side. Along the foot of the islands runs a straight horizontal groove, known as a wave-cut notch. It is the mark of an ancient sea level. Each such groove is a page of geological history, written into the stone.

But Ha Long is not only a story of geology. People have lived here for at least 18,000 years. Archaeologists have found evidence of three prehistoric cultures, one following another. The Soi Nhụ culture lasted from 18,000 to 7,000 years ago. Its people lived in caves in the limestone islands and used rough stone tools. The Cái Bèo culture lasted from 7,000 to 5,000 years ago. Its people settled along the shore, lived from the sea, and made finer pottery. The Ha Long culture came later, from 4,500 to 3,500 years ago. It had a thriving seafaring economy, finely worked stone tools, and pottery shaped on a wheel.

In 1149, Emperor Lý Anh Tông founded the trading port of Vân Đồn in these waters. It became a major international trading center of Đại Việt, an old name for Vietnam. It traded with Japan, China and Southeast Asia.

These waters are also tied to three great victories of medieval times. In 938, on the Bạch Đằng River, Ngô Quyền defeated the army of the Southern Han, a Chinese kingdom of that time. In 981, Lê Hoàn defeated the army of the Song, the dynasty then ruling China. In 1288, Trần Hưng Đạo fought off the armies of the Yuan, the Mongol dynasty then ruling China.

There is an old legend about the name Ha Long. The Jade Emperor sent a Mother Dragon and her Dragon Children down to earth, to help the Vietnamese people fight off their enemies. The dragons spat out precious jewels, and the jewels became thousands of rocky islands. The place where the Mother Dragon came down was called Ha Long, which means descending dragon. The place where her children came down was called Bái Tử Long. And the place where the dragon tails thrashed was called Bạch Long Vĩ. This is a folk legend, not a historical event. But it reflects something true. This sea is so beautiful that people needed a magical story to explain it.

Ha Long Bay is home to nearly 3,000 species of plants and animals. Ten different kinds of ecosystems exist side by side here. They range from island forests, sheltered lagoons and caves to seagrass beds, coral reefs and mangrove forests. Seventeen plant species grow here and nowhere else on Earth.

A stalactite only 1 centimeter long can take from 100 to 200 years to form. The stone hanging overhead in Sửng Sốt or Thiên Cung began to grow long before any of us was born. It will still be there when all of us are gone.

340 million years to make these islands. Thousands of years for the first people to pull their boats into the shadow of the rocks, look up at the high cliffs, and know that this was the place they wanted to call home. And now, with waves lapping softly at the boat and towering cliffs catching the afternoon light, you are seeing what all of them saw: a sea so beautiful that it took a whole dragon story to explain it.