The wall went up at a particular moment of anxiety. Construction began in 1887 and was completed in 1889, during the late Qing Dynasty's administration of Taiwan — just six years before the Treaty of Shimonoseki would transfer the island and its outlying archipelagos, including Penghu, to Japan. The Qing authorities had reason to be concerned about Penghu's vulnerability. French forces had occupied the islands during the Sino-French War only two years before construction began, and the strategic value of the harbor was not lost on any of the regional powers circling the western Pacific.

The resulting wall was substantial: 2,762 meters in length, topped with 570 merlons — the raised sections of a battlement between which defenders could fire. Six gates controlled movement in and out of the city. It was a serious piece of defensive infrastructure, built to last.

Japan's administration of Taiwan, which began in 1895 and lasted through the Second World War, brought significant urban transformation to Magong. Colonial planners reorganized streets, expanded infrastructure, and made room for the administrative apparatus of a regional naval base — the Imperial Japanese Navy made Penghu a major installation, and the city grew to serve it.

In that process of modernization, the south wall, both southern gates, and the north and east walls and gates were torn down. The logic was practical: the walls impeded traffic, occupied land the growing city needed, and had no remaining military function in an era of naval artillery. That they also erased a physical layer of pre-colonial history was, in the priorities of that administration, secondary. The stones came down.

When Taiwan was transferred from Japan to the Republic of China in October 1945, the military perimeter west of the surviving wall segment became part of the Penghu Defense Command. The remaining structure found a new administrative identity: not a historical relic but an active boundary within a military zone.

At some point after the handover, the smaller west gate was restored to something close to its original form. It stands now as the most intact reminder of what the full circuit of walls once looked like — a single gate representing six, one restored entrance in place of the wall that once enclosed an entire city.

The fragments that survive carry the compressed history of Penghu itself: Qing anxiety about territorial security, Japanese colonial priorities, postwar military administration, and eventual heritage recognition by the Bureau of Cultural Heritage, Ministry of Culture. The wall did not survive intact because it was especially well protected; it survived in pieces because demolition stopped before it was finished, and because the fragment that remained happened to fall within a military zone that paused the usual pressures of urban development.

Today the Magong Old City Wall is recognized as a cultural heritage site. Visitors walking the surviving section and the restored west gate can trace the profile of a fortification system that once defined this city's boundary with the sea — before the sea, in a sense, became less of a threat than the streets pressing in from all sides.