La Mercè is an annual holiday that is idiosyncratic to Barcelona. It commemorates the Mother of Jesus; for she is the patroness of the city. The holiday has been celebrated since 1871 on the 24th of September every year, with a governmental program of special activities.
It is believed that the Virgin Mary appeared to King James of Aragon and St. Peter Nolasco in the 13th century, and plead them to create a religious order denominated the Mercedarian Order – an endeavor to free the Christian captives from the Moors, regardless of the ramifications. The Mercedarian Order was not ceased after accomplishing its primary task; but rather, it continued to thrive.
In the year 1687, the governing council of Barcelona, after failing to put an end to the plague of locusts, prayed for Mary’s succor. The interposition of the Virgin Mary to relieve the city of the epidemic was recognized by the Mercedarian Order, and a feast day was established to commemorate and honor the Virgin Mary for her perpetual efforts in saving the city.