Go back in history and defend against the most deadly viruses such as Measles, Smallpox and Typhus. Start all the way back in 1200BC and learn about the different viruses along the way while you work your way up to the current time year. Battle against the falling viruses to protect your civilization from destruction. Update: Recently forced to delete a certain virus as Google has a policy that does not allow anyone except government/healthcare apps to mention it.