The approximate location and extent of the North March¹

In the early centuries after the War of the Last Alliance, the power of Gondor grew and its borders stretched far across Middle-earth, but it also suffered periodic assaults out of the East. Rómendacil I drove back one of these waves of attackers, and then sought to solidify his kingdom's defences. As part of this effort he fortified Anduin, and raised the Pillars of the Kings on Anduin to mark the northern extent of Gondor's power. Beyond these great statues of Isildur and Anárion, no stranger was permitted to enter Gondor from the northern lands. With the Argonath in place, the stretch of Anduin above Nen Hithoel and Rauros effectively marked Gondor's formal northern border. It was this region, running southward from the Argonath to the shores of Nen Hithoel and perhaps beyond, that was known as the North March (where a 'march' simply means a borderland).

At the end of the Third Age, the lands referred to as the North March lay far beyond Gondor's actual boundaries. Over a time of nearly 1,800 years since the Argonath were set to guard the Great River, the power of Gondor had waned considerably. At the time of the War of the Ring, Gondor's true North March was probably some hundred miles farther down the Great River, but the old border marked by the statues of the Argonath, though far beyond the land's true boundaries, was still referred to as the 'North March'.