Epic Citadel, the Unreal Engine 3 tech demo for iPhone and iPad, has been downloaded more than a million times.
The demo was only added to the App Store at the start of September following an Epic Games press event.
Epic Citadel offers a taste of not only what Unreal Engine 3 can deliver on iPhone, but what Project Sword - the game from which the demo was taken - will deliver.
Project Sword is a codename, by the way, and the game is being made by Chair Entertainment of Shadow Complex and Undertow fame. Project Sword will be released later this year.