Magnus Sinus

The Magnus Sinus or Sinus Magnus (Latin; ὀ Μέγας Κόλπος, o Mégas Kólpos), also anglicized as the Great Gulf, was the form of the Gulf of Thailand and South China Sea known to Greek, Roman, Arab, Persian, and Renaissance cartographers before the Age of Discovery. It was then briefly conflated with the Pacific Ocean before disappearing from maps. The gulf and its major port of Cattigara had supposedly been reached by a 1st-century Greek trader named Alexander, who returned safely and left a periplus of his voyage. His account that Cattigara was "some days" sail from Zaba was taken by Marinus of Tyre to mean "numberless" days and by Ptolemy to mean "a few". Both Alexander and Marinus's works have been lost, but were claimed as authorities by Ptolemy in his Geography. Ptolemy (and presumably Marinus before him) followed Hipparchus in making the Indian Ocean a landlocked sea, placing Cattigara on its unknown eastern shoreline. The expanse formed between it and the Malay Peninsula (the "Golden Chersonese"), he called the Great Gulf. Ptolemy's Geography was translated into Arabic by a team of scholars including al-Khwārizmī in the 9th century during the reign of al-Maʿmūn. 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. African traders similarly showed that the coastline did not turn sharply east south of Cape Prasum below Zanzibar as Ptolemy held. Al-Khwārizmī's influential Book of the Description of the Earth, therefore, removed Ptolemy's unknown shores from the Indian Ocean. The robustly-described lands east of the Great Gulf, however, were retained as a phantom peninsula (now generally known as the Dragon's Tail). Just after 1295, Maximus Planudes restored Ptolemy's Greek text and maps at Chora Monastery in Constantinople (Istanbul). This was translated into Latin at Florence by Jacobus Angelus around 1406 and quickly spread the work's information and misinformation throughout Western Europe.