The Gryphon was a being made by aliens out of artificial stars. It came to Babylon on Earth in 905 B.C. and took the form of a constellation, named the Gryphon by Urtaki.
The Gryphon became manifest after dark, and began an attack on the city before being trapped by the reflective power of mirrors. Cut off from its operator, the Gryphon construct vanished several hours after capture once the sun had risen. It left behind an armful of silver disks that were safely collected up and taken away by the Doctor and Amy Pond in the TARDIS. (DWAM: In the Stars)