Strabo Geography 16.4.22

[22] The late expedition ¹ of the Romans against the Arabians, under the command of Aelius Gallus, has made us acquainted with many peculiarities of the country. Augustus Caesar despatched this general to explore the nature of these places and their inhabitants, as well as those of Ethiopia; for he observed that Troglodytica, which is contiguous to Egypt, bordered upon Ethiopia; and that the Arabian Gulf was extremely narrow, where it separates the Arabians from the Troglodytae. It was his intention either to conciliate or subdue the Arabians. He was also influenced by the report, which had prevailed from all time, that this people were very wealthy, and exchanged their aromatics and precious stones for silver and gold, but never expended with foreigners any part of what they received in exchange. He hoped to acquire either opulent friends, or to overcome opulent enemies. He was moreover encouraged to undertake this enterprise by the expectation of assistance from the Nabataeans, who promised to co-operate with him in everything.