Short answers, pulled from the story.
Vatican City became an independent state on the 11th of February 1929, when the Lateran Treaty was signed by Cardinal Secretary of State Pietro Gasparri for Pope Pius XI and by Prime Minister Benito Mussolini on behalf of King Victor Emmanuel III. The treaty was ratified and took effect on the 7th of June 1929.
Vatican City is a sovereign city-state of 43.9 hectares created in 1929 to give the Holy See a physical territory and temporal independence. The Holy See is the central governing body of the Catholic Church, a distinct juridical entity that has existed since Roman Imperial times and retained international recognition even between 1870 and 1929 when it held no territory.
Vatican City has an area of 43.9 hectares and a population of about 882 residents as of 2024, making it the smallest sovereign state in the world both by area and by population. It is the only country in the world with a population under 1,000 people.
Pope Julius II founded the Pontifical Swiss Guard on the 22nd of January 1506 as his personal bodyguard. Recruits must be Catholic, unmarried Swiss males between the ages of 19 and 30, at least 174 centimeters tall, and must have completed basic training with the Swiss Armed Forces.
Vatican City grants citizenship on the basis of jus officii, meaning appointment to a specific role in service of the Holy See, not by birth within the territory or by descent from a citizen. Citizenship typically ends when the appointment ends, and anyone who loses Vatican citizenship without holding another nationality automatically becomes an Italian citizen under the terms of the Lateran Treaty.
Vatican City contains St Peter's Basilica, designed by architects including Bramante, Michelangelo, Carlo Maderno, and Gian Lorenzo Bernini, and the Sistine Chapel with frescos by Perugino, Domenico Ghirlandaio, Sandro Botticelli, and Michelangelo's ceiling and Last Judgment. The Vatican Apostolic Library and Vatican Museums hold collections of major historical, scientific, and cultural importance; the entire Vatican was added to the UNESCO World Heritage List in 1984.