On January 22, 1506, the first contingent of 150 Swiss Guards arrived at the Vatican. From the article:
"Swiss Guards | Overview, History, & Facts
Alternative Title: Guardia Svizzera
Swiss Guards, Italian Guardia Svizzera, corps of Swiss soldiers responsible for the safety of the pope. Often called “the world’s smallest army,” they serve as personal escorts to the pontiff and as watchmen for Vatican City and the pontifical villa of Castel Gandolfo.
Swiss mercenaries were long renowned as the best soldiers in the world—the ancient Roman scholar Tacitus stated, “The Helvetians are a people of warriors, famous for the valour of their soldiers”—and they served the ruling powers of many European countries; they were in particularly high demand in France and Spain. The guardsmen began serving the Papal States in the late 14th and 15th centuries. In 1505 the Swiss bishop (later cardinal) Matthäus Schiner, acting on behalf of Pope Julius II, proposed the creation of a permanent Swiss contingent that would operate under the direct control of the pope, and on January 22, 1506, the first contingent of 150 Swiss guardsmen, led by Captain Kaspar von Silenen, arrived at the Vatican. They soon earned a reputation for self-sacrifice and bravery, as demonstrated during the sack of Rome in 1527, when all but 42 of the 189 guardsmen died defending Pope Clement VII. The Swiss Guards prepared for similar self-sacrifice during World War II, when the vastly outnumbered guardsmen took up defensive positions as German forces rolled into Rome; Adolf Hitler, however, chose not to attack the Vatican.
The unit was reorganized in 1914 to consist of a commandant (with the rank of colonel), 5 other ranking officers, 15 lesser officers, a chaplain, and 110 pikemen. Further reorganizations were made in 1959 and 1976, and in 1979 their number was fixed at 100 (a commandant, 3 other high officers, a chaplain, 23 lesser officers, 2 drummers, and 70 pikemen).
In 1981 Swiss Guards helped protect John Paul II during an assassination attempt in St. Peter’s Square. In fact, the plainclothes guardsman who rushed to the pope’s aid became a hero and was named commandant of the Swiss Guards in 1998. Within hours of his promotion, however, he and his wife were shot and killed by a disgruntled lower-ranking guard, who then committed suicide; these were the first murders known to have taken place in Vatican City since the mid-19th century.
The Swiss Guards are sometimes referred to as the Vatican City police, but a separately administered police force is charged with the overall security of the nation-state (except St. Peter’s Square, which is under the jurisdiction of the Italian police)."