Call of Duty started off as a World War shooter before it shifted its focus to modern combat and futuristic guns. Interestingly enough, there was a point in time where the franchise was on the verge of heading to the distant past before guns were ever invented.
Following the success of Call of Duty 4: Modern Warfare and around the time World at War was released, Activision started investigating ideas to move the series forward. Activision asked developers to be as creative as possible, so developer Vicarious Visions (famous for Skylanders) created a prototype for a Call of Duty game that takes place in ancient Rome.
Call of Duty: Roman Wars would start with the player controlling a soldier in Julius Caesar's Tenth Legion then going through several protagonists culminating to play as Julius Caesar himself. Gameplay was set to mix between third and first person combat.
The prototype went all the way up to CEO Bobby Kotick and it was positively received by most of the high brass before it was shot down by a mixture of studio stubbornness and fears of over-saturating the brand.
VIA: GamesRadar.