Vatican city is a sovereign state within the city of Rome. It became a state in 1929. Its size is only 110 acres, the smallest country in world. It's the size of a typical small residential ranch in Texas.
And I tell you, you are Peter and on this rock I will build my church and the gates of Hades will not prevail against it. Matthew 16:18
There are two security forces that protect the Vatican City State;
The Corps of Gendarmerie of Vatican City handles border control and criminal investigations.
And the Swiss Guard, trained in Switzerland, is the personal security force of the Pope.