Achaemenid Arabia corresponded to the lands between Nile Delta (Egypt) and Mesopotamia, later known to Romans as Arabia Petraea. According to Herodotus, Cambyses did not subdue the Arabs when he attacked Egypt in 525 BCE. His successor Darius the Great does not mention the Arabs in the Behistun inscription from the first years of his reign, but does mention them in later texts. This suggests that Darius might have conquered this part of Arabia.
Arabs were not considered as subjects to the Achaemenids, as other peoples were, and were exempt from taxation. Instead, they simply provided 1,000 talents of frankincense a year. They also helped the Achaemenids invade Egypt by providing water skins to the troops crossing the desert.