Vatican City is the European country whose square yellow-and-white flag bears crossed keys and a papal tiara.
The flag is divided vertically, with yellow at the hoist and white at the fly. The white half carries the emblem of the Holy See: the papal tiara above the crossed keys of Saint Peter. The keys represent the Catholic tradition of Saint Peter’s authority and the Church’s spiritual and temporal responsibilities.
Vatican City adopted the design in 1929, the year the Lateran Treaty created the independent Vatican City State. Its colours and layout descend from the yellow-and-white flags used by the Papal States, particularly a design used from 1825 until the Papal States were annexed by Italy in 1870.
The flag is notable for its 1:1 proportions, making it square. Switzerland is the other sovereign state whose national flag is commonly square. The flag of Vatican City is often confused with papal or Holy See flags, but the Vatican flag is the state’s national symbol.