New recruits to the Pope's bodyguard have sworn loyalty to him in their annual May 6 ceremony. The date marks the Sack of Rome in 1527, when 147 Swiss Guards died defending Pope Clement.

While their traditional armour and colourful uniforms – actually designed in 1914 – make them a popular tourist attraction today, they are highly-trained soldiers who use modern weapons including pistols and submachine guns and their everyday uniform is far more functional.

Swiss mercenaries became a byword for loyalty and courage from the 15th century onwards, when young men sought their fortunes abroad in military service. Today's recruits have to be Swiss citizens, Catholics, of good character and have undergone military training in Switzerland. They must be unmarried, with a degree or professional diploma and be over 174 cm tall.

According to the Aleteia news service, the guards began their day by attending mass in St Peter's Church. Vatican secretary of state Cardinal Pietro Parolin referred to the events of 1527 and said that "such a heroic death...would not have been possible without faith in the Lord of Life". He continued: "Sustained by this faith in the Risen Jesus, and strengthened by the experience of joy that the Lord gives life in fullness, I invite you, dear Guards, to have the courage to be witnesses in the world today, despite the difficulties.

"Be witnesses of Christ – even in your own homeland, Switzerland – and in a world that desires light and life but often does not have the courage to accept it, in the midst of your young peers, who hunger for meaning and fulfillment, so that you may tell them that it is worth proposing great and beautiful things, although this involves commitment, dedication and will require some toil."

A later ceremony takes place in the St Damaso Courtyard in Vatican City, in the presence of the guards' relatives and friends and representatives of the Swiss Confederation. They swear an oath to serve and protect the Pope and his successors and promise obedience to their superiors: "I swear I will faithfully, loyally and honorably serve the Supreme Pontiff Francis and his legitimate successors, and also dedicate myself to them with all my strength, sacrificing if necessary also my life to defend them."