Casthenid was founded in the early Third Age near an old Númenórean fort guarding the Greyflood and quickly grew wealthy. Eventually, the fort was transformed into a fortified mansion, and a palace was built next to it. After the split of the kingdom of Arnor, it became part of the kingdom of Cardolan.
The war against Angmar led most of the inhabitants to desert the town. The remaining population was decimated by the Great Plague in T.A. 1636, leaving the remains of the town to ruin. The great flood of the Long Winter in T.A. 2912 completely erased the lower town and harbour.