This ritual was born from the tale of St. Jordi (St. George). The legend takes place in the town of Mont Blanc, where apparently a ferocious dragon had lived hundreds of years ago. To keep the town safe, every month the townspeople had to draw the name of a virgin girl to sacrifice.
A huge problem erupted in the town when the princess name was drawn. The king protested and demanded a redraw, because after all she was the princess, and consequently, should be exempted. The town’s people disagreed, and thus so, the princess was set for the dragon’s next meal...
A knight by the name of St. Jordi, was travelling nearby at the time, and got word of this. Jordi, being a noble night, was determined to rescue the princess from a horrible fate. When Jordi found and sleighed the dragon, it’s said that the blood that soaked the ground formed a beautiful red rosebush. After rescuing the princess, apparently Jordi then picked a rose from this bush and gave it to the princess. And thus was bron the tradition of St. Jordi.