The Vatican City is a landlocked sovereign city-state, consisting simply of a walled enclave inside of Rome's city limits. Its size is just over 100 acres, and its population level pushes 800, making it the smallest independent state on Earth in both cases. It's set on Vatican Hill, a few hundred meters west from the Tiber River. Its borders were originally set up to protect the Pope from being attacked from the outside. St. Peter's Basilica can be admired here.