Many think the stone was moved at least once and then later was rediscovered yet again.  Even within the last 15 years there has been controversy between countries over this artifact.

Here is more on its fascinating background from wikipedia:

The Rosetta Stone is a granodiorite stele inscribed with a decree issued at Memphis, Egypt, in 196 BC on behalf of KingPtolemy V. The decree appears in three scripts: the upper text is Ancient Egyptian hieroglyphs, the middle portion Demotic script, and the lowest Ancient Greek. Because it presents essentially the same text in all three scripts (with some minor differences among them), the stone provided the key to the modern understanding of Egyptian hieroglyphs.

We hope you like the video and feel free to comment with any of your theories!