In Arabia, Bahrain, which was referred to by the Greeks as Tylos, the centre of pearl trading, when Nearchus came to discover it serving under Alexander the Great. The Greek admiral Nearchus is believed to have been the first of Alexander's commanders to visit these islands. It is not known whether Bahrain was part of the Seleucid Empire, although the archaeological site at Qalat Al Bahrain has been proposed as a Seleucid base in the Persian Gulf. Alexander had planned to settle the eastern shores of the Persian Gulf with Greek colonists, and although it is not clear that this happened on the scale he envisaged, Tylos was very much part of the Hellenised world: the language of the upper classes was Greek (although Aramaic was in everyday use), while Zeus was worshipped in the form of the Arabian sun-god Shams. Tylos even became the site of Greek athletic contests.