Tolkien gives us no explicit dates for Thranduil, so we need to rely on circumstantial evidence. Thranduil's earliest mention is in Appendix B to The Lord of the Rings, where we're told that he was among the Sindar who travelled eastward from Lindon 'before the building of the Barad-dûr'. Sauron started building the Barad-dûr in about II 1000, so Thranduil must predate this.
We last hear of him soon after the Dark Tower's final overthrow. On 6 AprilIII 3019, (the Elves' new year), he met with Celeborn under the boughs of Mirkwood. Though we never hear of him after this date, the purpose of the meeting was to define the kingdoms of the two lords. It seems likely, therefore, he would have ruled in the newly renamed Eryn Lasgalen for some time after this.</td>
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2
<p>Tolkien's reticence on the meaning of Thranduil's name needn't prevent us from indulging in a little guesswork. One reasonable possibility for the name's source would be tharanduil, a combination of elements that means 'beyond the long river'. Though this is no more than speculation, Thranduil's history of travelling eastward from Lindon and ruling a kingdom across the Great RiverAnduin lends it some small credibility.
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The text of Appendix B to The Lord of the Rings seems to imply that Thranduil was himself the founder of the kingdom of Elves in Greenwood the Great. However, later writings challenge this assumption, suggesting that Thranduil travelled eastward with his father, who was the original ruler of the woodland realm. According to this source, Thranduil did not become king until the loss of his father in the War of the Last Alliance at the end of the Second Age.
