Argeleb I (S. "Silver King") succeeded his father Malvegil as the seventh King of Arthedain in T.A. 1349 at an age of 123. When Argeleb ascended to the throne in Fornost, he was certain the royal line of Isildur had died out in Rhudaur, and appeared to have also perished in Cardolan at this time, he reclaimed sovereignty over all three northern kingdoms, taking the royal prefix "Ar-" as a token of this in his name and declared himself the King of Arnor.
With his reign marking the beginning of Arthedain's claim to Cardolan and Rhudaur, troubles would come from both of those regions. Angmar had effectively taken control of Rhudaur, and Arveleg's claim aggravated many of the petty Princes in Cardolan. Some of these princes claimed to have the blood of Isildur in their lines and refused to recognize Argeleb's lofty claim. Argeleb would invite them to Amon Sûl to present their hereditary claims, but before this took place, Argeleb was soon encumbered by probing attacks from Rhudaur while the defiant princes of Cardolan attempted to back their claims with verifiable proof.
Argeleb, along with being a skilled soldier and commander, was also an accomplished scholar and had studied architecture. He reaffirmed his father's order for the continued building of fortresses and castles fortifying Arthedain's frontiers, and several watchtowers were built along the Weather Hills. The Witch-king, receiving word that Arthedain's strengthening of their defenses was not yet complete, planned to unleash his armies of Orcs and Hillmen from the Ettenmoors.
In the fog of the early morning in the spring of T.A. 1356, The Witch-king attacked in force. Arthedain held initially, and Argeleb rallied his army as he brought reinforcements. Many Princes of Cardolan had ridden to Arthedain's assistance, but a few had secretly allied themselves with Rhudaur.
After weeks of fighting, Argeleb planned a counterattack, but stealth Hillman warriors from Rhudaur infiltrated the Arthedainian position, and the following attack was devastating. Argeleb's son Arveleg, managed to retreat from Amon Sûl with the Palantir, but Argeleb was surrounded, and he along with an allied Prince of Cardolan and their regiments were slain to a man.
Argeleb I had only ruled Arthedain for seven years, and was succeeded by his son Arveleg I. The battle was costly, but the losses to the army of Angmar were such that they could not pursue Arveleg, and Arthedain again reoccupied their fortresses in the Weather Hills.