The fort was built in 1629, on the site of an artillery battery that had been thrown up in the immediate aftermath of the Battle of Macau in 1622 — a Dutch naval assault that the Portuguese repelled, but only barely. The lesson was clear: the inner anchorage needed permanent, serious defense. The Portuguese engineers built low to the water, placing bulwarks and gun platforms close to sea level so that warships passing through the channel would have no room to maneuver. They also blocked much of the channel itself, forcing any hostile vessel to sail directly past the fort's guns. Additional platforms were constructed up the hill to command the higher angles. It was a compact, thoughtful piece of military engineering for its era.

Like most of Macau's colonial fortifications, Fort São Tiago da Barra spent long stretches in quiet decline. The threat from European rivals faded; the fort's strategic purpose diminished; maintenance lapsed. By the time of the Second World War, the old cannon still sitting on the ramparts were not symbols of power — they were an asset that could be liquidated. Portuguese Macau sold them for scrap metal to buy rice for refugees streaming in from Hong Kong and occupied mainland China. It was a practical decision made under real pressure, and it stripped the fort of its most visible military artifacts. The walls remained, but the weapons were gone.

The fort survived into the present in an unusual form: in 1981, the Portuguese converted it into the Pousada de São Tiago, a boutique hotel of twelve suites built into and around the old military structure. Guests sleep within the fort's thick stone walls, looking out over the Inner Harbour. The chapel inside remains the heart of the site: it holds an image of the Virgin and the statue of the patron saint for whom the fort is named — the same São Tiago said to patrol the walls after dark. In front of the fort stands an armillary sphere, relocated from Senate Square, its brass rings a relic of the Portuguese navigational tradition that brought these colonists to the Pearl River Delta in the first place.

Fort São Tiago da Barra is part of the Historic Centre of Macau, a UNESCO World Heritage Site encompassing the layered remnants of Portuguese colonial rule in China. The Barra Hill area, where the fort sits, is one of the oldest sections of Macau — the A-Ma Temple nearby predates the Portuguese arrival entirely, speaking to the much longer Chinese history of the place. The fort thus occupies a border zone: a piece of European military architecture in a Chinese city, now a monument inside a Chinese special administrative region, still watched over by a saint whose boots, according to tradition, are never quite clean.