Paris is worth a mass: how many times have we heard this expression without immediately remembering  who had said it and without knowing why we still say it.

“Paris vaut bien une messe”  was said by Henry III, king of Navarre who decided to go mass and so to become Henry IV, King of France (1553-1610). Henry of Navarre was the first in line in succession to the French king, who had died without leaving heirs. The problem of succession was very complicated though, since Henry of Navarre was a Huguenot (Protestant) and France had to have a Catholic king. So for the goodwill of France and in order to become king, Henry agreed to change his religion and so to go to mass in Paris. This expression remained in the speach meaning a "moral" sacrifice that sometimes must be done to achieve a certain goal. Henry IV was the founder of the Bourbons dynasty that was the one of the last kings of France, since it was his descendant Louis XVI, that had to be executed by guillotine.

Henry married twice. The first with Marguerite de Valois, Margot (sister of the King of France and daughter of Catherine de Medici) and then, because their marriage was annulled because they did not have any children,  with Maria de Medici (in 1600), niece of Ferdinand I, Grand Duke of Tuscany.
On May 14th , 1610 Henry IV was assassinated in Paris. His son, Louis XIII, was still a child and so his wife, Marie de Medici, who had been crowned Queen just the day before, was appointed regent.
On hearing this bad news the young Grand Duke Cosimo II Medici decided to have very solemn celebrations to pay homage to the French king and this way reaffirm his and Tuscany’s bonds with his cousin, the Queen of France.
At the Medici Chapels from  you can see what was used for these celebrations, many paintings, books, prints and drawings that celebrate Henry IV and Louis XIII, including a magnificent Rubens and much, much more.