The Vatican
The agreement between Mussolini and the Catholic Church is known as the Lateran Treaty, you may read about it at the first link below, and see it at the second link.
Lateran Museum ended in 1970.
Lateran Museum was created in 1844.
Lateran Palace, Rome
Fifth Council of the Lateran ended in 1517.
Fifth Council of the Lateran was created in 1512.
Papal Lateran Cross was created on 1903-02-18.
Lateran Treaty
Vatican City was formed with the signing of the Lateran Treaty in 1929 by Pope Pius XI and Benito Mussolini.
Please see the related question.
Please see the related question.