text: The Transcaucasus is bordered on the north by Russia , on the west by the Black Sea and Turkey , on the east by the Caspian Sea , and on the south by Iran .
simplified: The Caucasus or Caucasia is a region in Eurasia bordered on the south by Iran , on the southwest by Turkey , on the west by the Black Sea , on the east by the Caspian Sea , and on the north by Russia .