The Ogre of Hyfor Three was a large, silicon-based lifeform which invaded Earth in the 3rd century. It was defeated by the Tenth Doctor in the year "AD two hundred and something".
The oversized foot of the Ogre was on display in the British Museum in the early 21st century. The accompanying placard claimed that the foot was from a colossal acrolithic statue. (PROSE: The Stone Rose)