The rune-inscribed bark of the Tree of Inifuss, the Scroll holds the key to open the way to Tristram by accessing the Cairn Stones in the Stony Field.
This scroll allows players, once it's translated by Akara, to touch the Cairn Stones in the prescribed order. When all the stones have been touched and activated, a red Portal to Tristram appears. Note that you don't have to touch the stones in the right order without making 'mistakes'. You can just frantically click every stone until they all start glowing, without even taking a glimpse on the Scroll. You can't activate the Cairn Stones without having reached the Tree of Inifuss though.