At this point the pass of the Orfalch was blocked by a wall of black iron, with four towers watching over the road as it climbed toward the Gate. Between the two central towers was a huge iron Eagle, representing Thorondor alighting on a mountain peak. Within the wall was a complex of three separate iron gates, one after the other, and each was formed in the shape of twisting forest trees with writhing roots and entwined branches. The effect of looking through these three gates together was said to appear remarkably like the view through a tangled forest in moonlight. From these twisting tree limbs on the Fourth Gate, it took its name of 'Gate of Writhen Iron'.
Behind the Gate of Writhen Iron was its own detachment of dedicated soldiers, the Iron Guards. These Elves wore black mail armour, and each carried a black shield and wore a helmet formed in the shape of an Eagle's beak. Beyond the Iron Gate and its Iron Guards, the steep path of the Orfalch Echor levelled out as it passed on through the mountains. From here the roadway ran past a green sward dotted with the flowers known as uilos and onward towards the Fifth Gate, the Gate of Silver.
Notes
1
The word 'writhen' here apparently refers not to the iron of the Gate, but to the twisting tree-shapes represented there. Indeed, the worked trees that decorated the Gate are described as having '...writhing roots and woven branches...' (Unfinished Tales Part One I, Of Tuor and his Coming to Gondolin), so giving the Gate of Writhen Iron its name.