Scroll of Isildur

The Scroll of Isildur was a scroll made by Isildur himself during his short time in Minas Tirith after the War of the Last Alliance between S.A. 3441 and T.A. 2. The scroll held Isildur's account of the gaining of the Ring from Sauron and described the appearance of an inscription around the Ring while it was still hot. The Scroll was stored for millennia in the vaults of that city and according to Gandalf it was probably forgotten after the time of the Kings of Gondor and nobody, except him and perhaps Saruman, had seen it.
Gandalf started to believe that Bilbo Baggins' Magic Ring was the One. In T.A. 3017 he visited Minas Tirith and studied the scroll. Isildur's description was vital in helping Gandalf identify the Ring. He visited Frodo Baggins in Bag End and tested his ring in the fireplace, confirming it as the One Ring of Sauron.