In those days the sceptre still passed to the eldest son of the king - if he had one - but Valandil, the son of Silmarien, became the first Lord of Andúnië. The royal houses of Arnor and Gondor derive their origins from his descendant Elendil, the eighteenth and the last Lord of Andúnië.
According to the genealogical table in UT 210 Valandil was born in S.A. 630. In the story of Aldarion and Erendis Valandil is told to have held a feast in ca. S.A. 700 to celebrate the 100th anniversary of the Guild of the Venturers (UT 182) and another feast for Aldarion and Erendis after their wedding in S.A. 870 (UT 189). The year of his death is unknown.
Valandil's wife is mentioned in UT 182 ('Erendis --- sat beside the wife of Valandil') but not named.
UT = Unfinished Tales.
Valandil, the third son of Isildur, was born in the very year, when the Last Alliance of the Men and the Elves was formed and the war against Sauron begun. He was kept in Rivendell during the war, and after Isildur's elder sons, Elendur and Aratan had fallen in the Battle of the Gladden Fields and Isildur had perished in Anduin in T.A. 2, he was the only heir to the throne of Arnor. (Anárion, the eldest son of Isildur had fallen already in S.A. 3440 during the siege of Barad-dûr; his son Meneldil become King of Gondor).
Valandil ascended the throne of Arnor in T.A. 10 at the age of 20 years. He died in T.A. 249 at the age of 260 years.
--Tik 13:58, 13 Jun 2005 (EDT)