This is the highest profile event of an annual 9-day festival of 'San Fermin', which begins each year at noon on July 6th and runs through midnight on July 14th.
Saint Fermin is a Catholic saint who is the patron saint of the city of Pamplona. He was said to have been martyred by having his body drug through the streets by bulls.
The current festival has it's roots in a secular festival previously held in June, and later moved to September, known as the Sanfermines.
The bull runs began in the area as far back as the 13th century. Cattle merchants would come to town for commercial festivals to celebrate the beginning of summer, and bullfights became central to the celebrations.
The runs custom traces it's origins back to the process of transporting bulls from their off-site corrals to the bullring for those bullfights. During this process, youngsters would jump in among the bulls as they were being moved in order to show their bravery. The celebration was finally formally established to the month of July in 1592.
