In the age of sail, Wuzhu Island ( 烏豬島), to the east of Shangchuan ( 上川島), was a major point of orientation for ships proceeding back and forth between Southeast Asia and various locations along the shores of central Guangdong. There was no permanent settlement on Wuzhu, but the island provided water and Chinese sailors associated it with a protective deity. One part of the sea in the area around Wuzhu was called Wuzhuyang ( 烏豬洋). However, its precise extension and limits remain unknown. A third toponym, Wuzhumen ( 烏豬門), leads to further questions. The article discusses selected references to these places and various nearby islands recorded on maps and in nautical and other texts of the Ming period. It also considers additional spaces mentioned together with the Wuzhuyang. A further focus is on Portuguese sources. In these works, Wuzhu Island appears under a Malay name: Pulau Babi. The analysis of this material confirms the impression provided by Chinese texts and maps, namely that Wuzhu/Pulau Babi was an important landmark in nautical contexts.