Great Fens

At one time, the western lands that would later be known as Minhiriath and Enedwaith were covered by a dense forest. There was almost no break the canopy of this ancient woodland, except for a stretch along the borders between the two regions, where the trees gave way to a wide wetland. Here the rivers Mitheithel and Glanduin ran down from the Misty Mountains and joined to form the wide river that would later be named Gwathló. Together these rivers formed a stretch of marsh known as the Great Fens.

In the later Second Age, the Númenóreans came to Middle-earth and began to fell the great forests. So widespread was their labour that they left Minhiriath and Enedwaith almost treeless, but the Great Fens in the central region remained. The river Gwathló proved ideal for transporting lumber to the coast, and so the Númenóreans established a settlement near the place where the rivers met. To accomplish this, they drained and managed the wetlands sufficiently to establish the town of Tharbad, with its famous Bridge crossing the upper Gwathló.

Standing at a key point on the route between the Kingdoms of the Dúnedain, Tharbad on the Great Fens remained important into the earlier Third Age, but in later years it fell into ruin and its Bridge was broken. Stretching eastward from the town, the Great Fens remained, filled with reeds and waterfowl. During the later Third Age, they were associated particularly with the lower course of Glanduin, being given the name of Nîn-in-Eilph or Swanfleet, the Waterlands of the Swans.