Lateran Treaty
Negotiations for the settlement of the Roman Question began in 1926 between the government of Italy and the Holy See, and culminated in the agreements of the Lateran Pacts, signed—the Treaty says—for King Victor Emmanuel III of Italy by Benito Mussolini, Prime Minister and Head of Government, and for Pope Pius XI by Pietro Gasparri, Cardinal Secretary of State, on 11 February 1929. It was ratified on 7 June 1929. The agreements were signed in the Lateran Palace, hence the name by which they are known.
Flag of Vatican City
The flag of Vatican City was adopted on June 7, 1929, the year Pope Pius XI signed the Lateran Treaty with Italy, creating a new independent state governed by the Holy See. The Vatican flag is modeled on the flag of the earlier Papal States. The Vatican (and the Holy See) also refer to it, interchangeably, as flag of the Holy See.