A harbor with an outlet merely 2.6 kilometers wide, yet an inland sea area of 614 square kilometers. Water depths of 10 to 50 meters — enough for 10,000-ton vessels to sail freely.

This is Sandu’ao. Geologists call it “one of the world’s rarest natural harbors.” But for five centuries, this world-class deep-water port was repeatedly sealed — from Ming Dynasty patrol boats, to the Qing Great Clearance, to scuttled ships during the War of Resistance.

I opened the Chronicles of the Funing Prefecture, the Annals of Fuzhou Customs, and the Annals of Ningde County. Between their yellowed pages, I traced the arc of this “gateway” from sealing to opening.

Geographic Connections

Sandu’ao, Ningde County (now Jiaocheng), Fu’an County, Xiapu County, Luoyuan Bay, Guanjingyang, Qingshanyang, Dongchong Entrance, Sandu Island, Guo’ao, Baima Port, Feiluan.

I. Natural Endowments of Sandu’ao: The Geometric Logic of a Deep-Water Giant

Sandu’ao lies in southeastern Ningde, Fujian. Its defining feature is a “narrow mouth, wide belly” — the Dongchong outlet is just 2.6 kilometers across, but opens into a vast interior basin.

1.1 Harbor Structure and Depth Data

The Chronicles of the Funing Prefecture records the inland sea area of Sandu’ao at 614 square kilometers. This semi-enclosed basin ensures tranquil waters, like a giant natural reservoir. Surveys from the 24th year of Guangxu (1898) showed depths between 10 and 50 meters, with an average tidal range exceeding 4.5 meters.

What does this mean? 10,000-ton vessels could enter and exit with ease.

1.2 Island Distribution and Natural Barriers

Sandu’ao is dotted with dense islands, creating “bays within bays, ports within ports.” The Annals of Ningde County counts 196 islands within the bay. The largest, Sandu Island, spans approximately 15 square kilometers. During the Wanli era of the Ming Dynasty, simple beacons were already built on the island.

This fragmented terrain was both a typhoon shelter and a natural ambush site for coastal defense.

II. The “Golden Sealing” of Ming and Qing: From Sea Bans to Strategic Reserves

Sandu’ao never became an international trade center despite its advantages. Instead, it was treated as a “gateway” to be guarded.

2.1 Tactical Value under Ming Sea Bans

In the 34th year of Jiajing (1555), wokou pirates raided Mindong. Sandu’ao’s seclusion made it a crucial anchorage for Qi Jiguang’s naval forces. The Military Annals of the Funing Prefecture records 12 patrol boats stationed at Guanjingyang and Dongchong.

Under the Ming sea ban, this world-class harbor was locked behind military lines. Civilian vessels were forbidden.

2.2 The “Great Clearance” and Restoration in Early Qing

In the 18th year of Shunzhi (1661), the Qing court ordered the “Great Clearance” to cut off Zheng Chenggong’s supply routes. All coastal residents of Sandu’ao were relocated 30 li inland.

For 22 years, Sandu’ao was nearly uninhabited. It was not until the 22nd year of Kangxi (1683) that coastal fishing gradually recovered. Only ruins remained on Sandu Island. During the Yongzheng era, with Mindong’s tea production booming, Sandu’ao’s value as a transshipment port was finally rediscovered.

III. 1898: Passive Opening and the Era of “Foreign Customs”

At the end of the 19th century, Sandu’ao reached its turning point from “sealing” to “opening.”

3.1 The Opening of Guangxu and Establishment of Customs

In the 3rd month of the 24th year of Guangxu (1898), the Qing government declared Sandu’ao a self-opened commercial port. On May 8, 1899, Fuzhou Customs established a sub-branch on Sandu Island — the “Sandu’ao Customs.”

According to the Annals of Fuzhou Customs, the opening year attracted consulates and firms from Britain, the USA, Japan, and Germany. The pier at Guo’ao was extended to over 150 meters.

3.2 Explosive Growth in Tea Trade

Sandu’ao’s opening activated Mindong’s tea exports. In the 29th year of Guangxu (1903), black tea (mainly Panyong Congou) exports through Sandu’ao reached 158,000 piculs — approximately 7,900 tons.

Closer to production areas than Fuzhou’s Mawei Port, Sandu’ao reduced logistics costs by 20%. In the early 1900s, annual customs revenue once exceeded 300,000 taels of silver, making it Fujian’s third-largest tax-collecting port after Fuzhou and Xiamen.

IV. Strategic Gambit under the Shadows of War

In the first half of the 20th century, Sandu’ao once again became a war front.

4.1 Desperate Defense during the War of Resistance

After the Marco Polo Bridge Incident in 1937, the Japanese military aimed to cut off Mindong’s sea routes. In May 1938, Japanese warships repeatedly invaded Sandu’ao, meeting fierce resistance from the Chinese navy.

The Military Volume of the Annals of Fuzhou City records 8 large-scale naval battles in Sandu’ao waters during the war. In 1939, the Chinese Navy scuttled 4 ships at the narrow Dongchong channel and deployed drifting mines, successfully slowing the Japanese advance.

4.2 Port Renaissance in the Modern Perspective

In the 1980s, Sandu’ao’s development returned to the agenda. In 1987, the State Council approved it as a first-class national open port. A 1992 large-scale nautical survey confirmed 3 major channels capable of accommodating 200,000-ton vessels.

From “sealed fortress” to “deep-water logistics hub” — Sandu’ao completed its transformation over five centuries.

V. Gateway Memories in Digital Gazetteers

From the first sentry posts of the Hongwu era of the Ming Dynasty to the rise of foreign customs in 1899 and the scuttled ships of the War of Resistance — the history of Sandu’ao is a microcosm of Mindong’s geography and global political currents.

The 614 square kilometers of sea and 300,000 taels of revenue recorded in these gazetteers are not just numbers. They are the pulse of a world-class deep-water port — the tides that never truly stopped.