Simplify the following text for a Grade 9 native English-speaking person.
Original: On the evidence of Lucian , the Parthians still held the southern , Roman bank of the Euphrates ( in Syria ) as late as 163 ( he refers to a battle at Sura , which is on the southern side of the river ) .
Simplified: On the evidence of Lucian , the Parthians still held the southern , Roman bank of the Euphrates ( in Syria ) as late as 163 .