The tradition of roses and books
In addition to the medieval tradition inspired by the legend of Saint Jordi, or Saint George, the custom of giving people roses on 23rd April has other origins. In the 15th century, Barcelona was already holding a delightful celebration known as the Fira dels Enamorats, or Lovers' Fair. On this day, rose sellers would set up stalls around the government building, the Palau de la Generalitat, and give the flower to the women going to mass in the chapel of Sant Jordi inside the building. There are historians who place the tradition much earlier and are certain that people were offering roses to the goddess Flora in the Roman era.
Giving a book on 23rd April is a later tradition that began in the 1930s to commemorate the death of Miguel de Cervantes (who actually died on 22nd April 1616 but was buried on 23rd April). Curiously enough, there are other world-famous authors who were either born or died on this date, such as William Shakespeare and Josep Pla.
In 1995, the 23rd April was declared World Book and Copyright day by UNESCO.