to explain a bit more... (spolier; sorry, don't know how to do these...)
From E of Arda
Path's of the Dead...A subterranean realm beneath the White Mountains above the valley of the River Morthond. The dwelling place through the Third Age of the Dead, Men cursed by Isildur for breaking their oath of fealty to him, and made to remain in Middle-earth until his rightful heir was to call for their aid.
Notes
1 Isildur laid a curse on the King of the Dead and his people that they would not rest until their broken oath to him was fulfilled, and that curse was the reason that these people haunted the Paths of the Dead. Isildur laid his curse before he went to war with Sauron, but he couched it in these terms: 'And if the West prove mightier than thy Black Master, this curse I lay upon thee and thy folk...' (The Return of the King V 2). The West did indeed prove mighter than Sauron, but not until II 3441, about eleven years after Isildur originally said these words.
It can't be stated with certainty that the Paths were occupied immediately after the curse took effect: their settlement may have taken years or even decades. Nonetheless, the curse that founded the Paths of the Dead took effect with the first Fall of Barad-dûr, hence the dating shown above.
2 8 March III 3019 is the date that Aragorn led the Dead out of their Paths towards the final fulfilment of their oath, after which the Paths of the Dead would be deserted. The Dead themselves continued to exist for several days, until they were released by Aragorn at Pelargir on 13 March.