If you had come to Guangzhou in the eighteenth century and looked from the Pearl River towards the shore, you would have seen a row of Western-style buildings — long two-storey blocks with colonnades, flying the flags of Britain, France, the Netherlands, Denmark, and Sweden.

This was the "Thirteen Hongs".

It was more than a place name. It was the Qing dynasty's only legal foreign-trade zone. From 1757 to 1842 — eighty-five years — almost all of China's porcelain, tea, and silk went out through here.

In 1757, the Qianlong emperor issued an edict: Western merchants were permitted to trade only at Guangzhou. All other ports were closed.

This was the "single-port" policy.

Why Guangzhou?

Because it was the best port in the south. Located at the mouth of the Pearl River, backed by the wealthy Pearl River Delta, with mature ocean routes and local merchants who had centuries of trade experience with Southeast Asia, the Middle East, and Europe.

More importantly: Guangzhou was far enough from Beijing. The court wanted foreigners kept at the empire's edge, away from the political centre.

The "Thirteen Hongs" were not thirteen firms. The name refers collectively to the licensed foreign-trade guilds in Guangzhou.

They were run by local Guangzhou merchants, officially called "foreign-goods houses" or "ocean houses". They were responsible for:

First, monopoly. Foreign merchants could not trade directly with the Chinese interior. They had to go through the Hong merchants. What to buy, what to sell, at what price — all mediated.

Second, customs. All import and export duties were paid on behalf of foreign merchants by the Hong merchants.

Third, surety. The Hong merchants vouched for the conduct of foreign merchants. If a foreigner defaulted or broke the law, the Hong merchant was liable.

In other words, the Hongs were simultaneously a trading company, a customs agent, and a guardian of foreigners.

This system saved the Qing government trouble: it did not have to deal with foreigners directly — only with a handful of firms.

Much of what we now call "export porcelain" or "Canton ware" was ordered through the Hongs.

The process went roughly like this:

Step one, the design. European merchants prepared the design they wanted — family crest, European landscape, mythological scene, chinoiserie flora and fauna — and handed it to the Hong merchants.

Step two, the order travels to Jingdezhen. The Hong merchants sent the order and sample to Jingdezhen. Potters there fired the blank porcelain or applied the base painting.

Step three, decoration in Guangzhou. The fired porcelain came back to Guangzhou. In workshops on the south bank of the Pearl River, Canton painters applied enamel and gilding. This is "Canton ware".

Step four, shipped out. The finished porcelain left from Whampoa, passed Macau, Malacca, and the Indian Ocean, and reached Europe.

The whole cycle, from order to delivery, usually took one to two years.

This is why many Chinese porcelains in European castles and English country houses carry Western coats of arms — they were not Jingdezhen's invention, but European custom orders.

In 1842, the Treaty of Nanjing was signed and five ports were opened. Guangzhou's monopoly ended.

Shanghai, Xiamen, Fuzhou, and Ningbo opened in turn. Foreign merchants had more choices; Guangzhou was no longer the only door.

The Hong system collapsed. In 1856, during the Second Opium War, the Thirteen Hongs factory district burned to the ground. Today, "Thirteen Hongs" is only a place name and a memory.

But the export porcelain it left behind became one of the most important material witnesses to East-West exchange.

Much of the "Canton ware" you see today in auction houses in Singapore, Hong Kong, and London came out of that eighty-five-year window.