It was founded at the end of First Age or in the early Second Age, when the Edain first migrated to the island. Conceivably, Arandor was the first district settled after landing in a firth on the island that later led to the haven of Rómenna.
Armenelos was the site of the royal palace known as the King's House, reportedly built with the help of the Maiar who ministered and taught the Edain before the official founding of Númenor. Its completion, together with the coronation of Elros Tar-Minyatur as the first King of Númenor in SA 32 marked the beginning of the Númenorean realm.
Armenelos is a Quenya word that translates as "Royal Fortress of the Heavens"