Excerpts from Books and Wikipedia
Admiral Zheng He commanded more than 27,000 sailors and soldiers. He visited Vietnam, Siam (Thailand), Malacca, Java, India, and Ceylon (Sri Lanka) over the next two years. The sailing voyages were ended after Zheng's death in 1435, probably because the emperor wanted to concentrate on defending his northern border. [Furtado: 1001 Days] Yet well before those explorers [Dias, da Gama, and Columbus] left their European ports--in the years between 1405 and 1433--Chinese Admiral Zheng He had taken an immense fleet west on seven voyages covering more than 100,000 miles, ranging as far as the Persian Gulf and Kenya. Zheng He's story is all the more remarkable considering that he was a commoner, a Muslim, and a eunuch. . . . A fourth voyage took him to the Persian gulf, where a Chinese mission visited Mecca." [National Geographic Almanac, p. 168-71]