 The tribes of southern Arabia asked the Persian king Khosrau I for aid, in response to which he came south to Arabia with foot-soldiers and a fleet of ships near Mecca.By the middle of the 6th century, there were three major settlements in northern Arabia, all along the south-western coast that borders the Red Sea, in a habitable region between the sea and the Hejaz mountains to the east.Although the area around Mecca was completely barren, it was the wealthiest of the three settlements with abundant water from the renowned Zamzam Well and a position at the crossroads of major caravan routes.