A monument comprising two enormous pillars carved in the likenesses of Isildur and Anárion, standing upon either side of the River Anduin at the northern approach to Nen Hithoel.
The figures were originally constructed about T.A. 1240 at the order of Rómendacil II[2] to mark the northern border of Gondor, although the realm was greatly diminished in size by the time the Fellowship of the Ring passed the Argonath on February 25, 3019.
Each of the two figures was shown wearing a crown and a helm, with an axe in its right hand and its left hand raised in a gesture of defiance to the enemies of Gondor.[3]
Also known as the Gate of Kings or the Pillars of the Kings.

Frodo peering forward saw in the distance two great rocks approaching: like great pillars or pinnacles of stone they seemed. Tall and sheer and ominous they stood upon either side of the stream. A narrow gap appeared between them, and the River swept the boats toward it.

“Behold the Argonath, the Pillars of Kings!” cried Aragorn. “We shall pass them soon. Keep the boats in line, as far apart as you can! Hold the middle of the stream!”

As Frodo was borne towards them the great pillars rose like towers to meet him. Giants they seemed to him, vast grey figures silent but threatening. Then he saw that they were indeed shaped and fashioned: the craft and power of old had wrought upon them, and still they preserved through the suns and rains of forgotten years the mighty likenesses in which they had been hewn. Upon great pedestals founded in the deep waters stood two great kings of stone: still with blurred eyes and crannied brows they frowned upon the North. The left hand of each was raised palm outwards in gesture of warning; in each right hand there was an axe; upon each head there was a crumbling head and crown. Great power and majesty they still wore, the silent wardens of a long-vanished kingdom. Awe and fear fell upon Frodo, and he cowered down, shutting his eyes and not daring to look up as the boat drew near. Even Boromir bowed his head as the boats whirled by, frail and fleeting as little leaves, under the enduring shadow of the sentinels of Númenor. So they passed into the dark chasm of the Gates.