One of the world's smallest professional armies, the Pope's Swiss Guard, has begun celebrations marking its 500th anniversary.

The celebrations began this morning with masses in Rome's Sistine Chapel and in the cathedral of Fribourg, in Switzerland, and an address to the full corps, assembled in St Peter's Square, by the Pope.

Pope Benedict recalled the historic arrival of the first guards and thanked the Swiss, speaking in French and German.

More celebration events will take place during the coming months, culminating with a contingent of ex-guards who will
re-enact the march of the first group, beginning in April.

They are expected to arrive in time for the annual swearing-in ceremony presided over by Benedict XVI.

The parade on that day usually takes place in the San Damasco Courtyard, but this year it will be in St Peter's Square for the first time.

History of the Swiss Guard

In the 15th and 16th centuries, thousands of young Swiss mercenaries enrolled in the armies of the fiefdoms, kingdoms and city states that were constantly at war in France, Italy and Germany during the early Renaissance.

During the reign of Empress Maria Theresa, about 250 to 450 soldiers from Switzerland were hired to guard the Hofburg, the winter palace in Vienna. They replaced previous military units that had performed that duty, and were later replaced by others. The oldest courtyard of the palace is still called the 'Schweizerhof'.

Francis I of France used some 120,000 Swiss levies in his wars, and in the battle of Pavia in 1525 his personal guard, the Hundred Swiss, were slain before Francis was captured by the Spanish.

Under Louis XIV, the Swiss troops were organized in two categories, with the Swiss Guard forming part of the King's military household, separate from twelve ordinary Swiss regiments of the line.

During the 17th and 18th centuries the Swiss Guards maintained a reputation for discipline and steadiness. Their officers were all Swiss and their rate of pay substantially higher than that of the regular French soldiers. The Swiss Guards were brigaded with the Regiment of French Guards and were in peace time stationed in barracks on the outskirts of Paris.

The most famous episode in the history of those Swiss Guards was their defense of the Tuileries Palace during the French Revolution. Of the nine hundred 'Gardes Suisse' defending the Palace on 10 August 1792 more than six hundred were killed during the fighting or massacred after surrender. An estimated two hundred more died in prison of their wounds or during the September Massacres that followed. The only survivors were a 300 strong detachment which had been sent to Normandy to escort grain convoys a few days before.

The French Revolution abolished mercenary troops in its citizen army, but Napoleon I and the Restoration Monarchy both used them. When the Tuileries were stormed again, in the July Revolution of 1830, the Swiss Guards melted into the crowd. They were not used again.

The Swiss constitution, as amended in 1874, forbade all military capitulations and recruitment of Swiss by foreign powers, although volunteering in foreign armies continued until prohibited outright, in 1927.

The Swiss Guard in the Vatican

Pope Julius II in 1505 asked the Swiss Federal Tagsatzung to provide him with a constant corps of 200 Swiss mercenaries.

In September of that year, a first contingent of 150 soldiers started their march towards Rome, under the command of Kaspar von Silenen, and entered the Vatican on 22 January 1506.

The force has varied greatly in size and has even been disbanded.

The Vatican guard's greatest moment of glory was probably on 6 May 1527, when all but 42 of 189 soldiers died fighting off the armies of Charles V, which attacked and overran the Vatican.

The surviving guardsmen ushered Pope Clement VII to safety via a hidden passageway.

Today, the Swiss Guard in Vatican City is an exception to the Swiss rulings of 1874 and 1927.

It is a small force responsible for the security of the Apostolic Palace, the entrances to the Vatican City and the safety of the Pope.

Would-be Guards must be Swiss citizens, faithful Roman Catholics with a 'good moral and ethical background,' unmarried, aged between 19 and 30 and at least 1.74m tall.

They must also have have completed high school or an apprenticeship, plus basic military service in the Swiss army, and be prepared to sign up at the Vatican for at least two years.

Famous for their colorful uniforms and medieval weapons, Guards don civilian clothes as part of the Pope's security detail when he travels.

They have also, especially since 1981, had extended training in unarmed combat and with issue SIG P 75 pistols and Heckler & Koch submachine-guns. Naturally, they continue to receive instruction in using the sword and halberd.

The force is specifically limited to one hundred soldiers and currently consists of four officers, 23 NCOs, 70 halberdiers, two drummers, and a chaplain, all with an equivalent Italian army rank.

The Swiss guards work side-by-side with another security force, the pontifical police.

Recent events

Two events have marred the recent history of this elite unit.

On 13 May 1981 an attempt was made to assassinate Pope John Paul II by Mehmet Ali Agca, a Turkish criminal who shot at the Pope in St Peter's Square.

During the incident, Alois Estermann, who had joined the Swiss Guard in 1980, jumped onto the moving Popemobile, shielding the pope with his own body.

Appointed Captain Commander of the Guard 17 years later, Colonel Estermann, his wife and a Guard, Cédric Tornay, were found dead less than a day later.

The Vatican's official report blamed Tornay for the killings, his motive being that he was upset about a reprimand for not returning to the barracks on time, and that he was not one of the guardsmen honoured by the pope.