Magnus Sinus

By that time, Arab merchants such as Soleiman had begun regular commerce with Tang China and, having passed through the Strait of Malacca en route, shown that the Indian Sea communicated with the open ocean.

As early as 1540, continuing exploration led Sebastian Münster to conflate the Great Gulf with the Pacific Ocean west of the Americas, supposing that the 1st-century Alexander had crossed to a port in Peru and safely returned.

The details of the Great Gulf changed somewhat among its various forms, but the ancient and Renaissance Ptolemaic accounts had it bound on the west by the Golden Chersonese and on the north and east by the ports of the Sinae, chief among which was Cattigara.

Believing the circumference of the Earth to follow Ptolemy's reduced figures or even smaller ones, cartographers during the early phases of the Age of Discovery expanded the Gulf to form the Pacific Ocean west of South America, considered to represent a southeastern peninsula of Asia.

Modern reconstructions agree in naming the Golden Chersonese a form of the Malay Peninsula but differ in their considerations of how much of the South China Sea to include within Ptolemy's reckoning of the Great Gulf.