The eleventh of Gondor'sKings, who succeeded his father KingAtanatar I during the waning years of the Third Age's first millennium. We know almost nothing of his reign, which seems to have been a peaceful one.
The date of Siriondil's birth appears only in The History of Middle-earth volume XII, The Peoples of Middle-earth. It cannot therefore be considered completely reliable.
At its simplest, Siriondil's name might be interpreted as 'devoted to Sirion', a reference to the mighty river that flowed through Beleriand in the First Age. The name Sirion means 'Great River', a title shared with the Anduin that flowed through Gondor. On balance, it seems more plausible that Siriondil's name refers to the Anduin that ran through his capital at Osgiliath, rather than the original Sirion, which had been destroyed thousands of years beforehand.