Legend of San Marco's rosebund

At the beginning of 9th century the doughter of the Doge Maria, fall in love with Tancredi a young guy with humble origins.

The Doge didn't look favorably the situation and hindered their relation. Maria advised her beloved Tancredi to go to battle against the Turks to gain the honor to compensate his poor origins by the glory of his feats. Tancredi actually fought valiantly and he distinguished himself among the other soldiers, but he was later mortally wounded and died over a rose garden.
But before he died he gave to his friend Orlando a rosebud soaked with his blood as a gift of love for his Maria. April 25, Maria was found dead on his bed holding the rosebud that had been delivered the day before.

According to this legend, since then on April 25th Venetians give a rose to their beloved woman.