Lastly, if we take this verse in conjunction with the previous two, we can see a person in Iran facing west towards Mecca as he prays, facedown beneath the fading sun. So we now have what appears to be a reference to Islam in a poem about time, death, night, and eternity. And through the twilight now the late Few travelers in the westward pass Kermanshah is a district and city in Iran. Here the poem further traces the path of the spreading darkness. The sun sets in the west, thus the west has often been seen as a symbol of death.
Death is a constant, thus furthering the idea of eternity and time.
In addition, to carry on the praying possibility brought up in the first stanza, death is the step that must be taken to get to ultimate reality and eternal reward or punishment. And through Arabia the edge Of evening widen and steal on Still further, the poet traces the path of the rising shadow across Arabia. If you take the stanza to say that the river is gone, then it repeats the same sentiment as stanza three where the poet mentioned the mountains changing. The river has dried up over time. If it is not the river but the bridge that is gone, then it can be taken to illustrate how human artifacts, as well as civilizations, crumble over time.