Before the ruin of Beleriand at the end of the First Age, the sea was narrow and ice-filled in the north, forming the strait of Helcaraxë, the Grinding Ice.
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Before the Second Age, Belegaer stretched from the Gap of Ilmen in the far north, where a bridge made of ice known as the Helcaraxë connected Middle-earth and Aman, to the far south, where it also connected with Ilmen and froze.