Shortly after the Egyptians stopped building pyramids, a large spaceship crashed into the Antarctic: breaking in half and getting lodged into the ice. There it sat. Until the planet warmed and broke a berg fee. The sentient ship now steadily collects "spare" metal parts to rebuild itself. Once intact, it will complete the mission it came to Earth to do...

Strength

Impenetrable hull.
Power source of unimaginable strength.

Strength Source
Advanced technology.