The precise date of the haven's founding is not recorded, but we do know that it was established by Aldarion during a voyage that preceded his recognition as the King's Heir. That event took place in II 800, so we can reliably date the founding of the haven to the later years of the eighth century of the Second Age.
The haven was originally known as the New Haven (Vinyalondë), but it had various other names throughout its history. It seems to have become known as the 'Great Middle Haven' some considerable time after its founding, because the 'Middle' of its name is relative to the Númenórean haven of Pelargir, far to the south. Pelargir was not founded until II 2350 (about 1,500 years after the Great Haven), so the name 'Great Middle Haven' cannot have appeared before that date.
The further history of the Great Middle Haven is not recorded in any detail. It still existed in some form at the end of the Third Age, and is marked on maps from that time, but by then it was long unused and had fallen into ruin.
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