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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 .
 Arabia, Red Sea, Hejaz
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Arabia, Red Sea, Hejaz