Tylos was the name used by the Greeks to refer to Bahrain, as the centre of pearl trading, when Nearchus came to discover it serving under Alexander the Great. From the 6th to 3rd century BC Bahrain was included in the Persian Empire by the Achaemenids, an Iranian dynasty. The Greek admiral Nearchus is believed to have been the first of Alexander's commanders to visit the island, and he found a verdant land that was part of a wide trading network; he recorded: “That in the island of Tylos, situated in the Persian Gulf, are large plantations of cotton tree, from which are manufactured clothes called sindones, a very different degrees of value, some being costly, others less expensive. The use of these is not confined to India, but extends to Arabia.” The Greek historian, Theophrastus, states that much of the islands were covered in these cotton trees and that Tylos was famous for exporting walking canes engraved with emblems that were customarily carried in Babylon.Ares was also worshipped by the country's indigenous and Greek population.
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.
The name Tylos is thought to be a Hellenisation of the Semitic Tilmun (from Dilmun). The term Tylos was commonly used for the islands until Ptolemy’s Geographia when the inhabitants are referred to as 'Thilouanoi'. Some place names in Bahrain go back to the Tylos era, for instance, the residential suburb of Arad in Muharraq, is believed to originate from "Arados", the ancient Greek name for Muharraq island.