Why do walls exist around cities or parts of countries? These attempts to keep invaders out – or inhabitants in – have a long history. The concept looms large in Donald Trump’s threats to build a barrier along the United States-Mexico border and in the fenced-off Israeli annexation of Palestinian territories. The cold war-era partitions between East and West Berlin are not such a distant memory.

China, too, has a long history of walling itself off from the rest of the world. The process continues in cyberspace, with the “Great Firewall Of China” not being an entirely facetious label. While the Great Wall of China is the best-known physical example, most Chinese cities have had external walls. Modern Xian and Nanjing retain magnificent stone and brick ramparts marked by superb entrance towers.

Beijing’s Ming-era city walls were once one of the capital’s crowning architectural glories. Their destruction in the 1950s, to create a series of massive ring roads, was an example of the Communist Party’s deliberate obliteration of national heritage. Fortunately, a few notable structures, such as Qianmen, were spared, and now stand marooned amidst the thundering traffic, like ghosts from another age.

Examples exist closer to Hong Kong. Among the least noticed of Macau’s historical sites are the city’s fragmentary walls, which – like those elsewhere in China – mostly date from the Ming period (1368-1644). From the 1630s until they were largely demolished in the 1860s, walls stood around what today is the city’s central area. For the first 70 years of Portuguese settle­ment after 1557, no substantial walls had existed around the newly established town; no one – Chinese or Portuguese – saw any need for them.

Walls were eventually built to deal with the expanding number of foreigners on the China coast. Macau’s city walls served two purposes: to keep newcomers out if they were troublesome; and, should their presence prove useful, as in the case of the Portuguese, to pen them in, like so much domestic livestock.