and i m alex marquardt in washington. next up we have the whole story with arnd cooper investigating the whole history of the running of the bulls. good night. every summer, cities across spain participate in a centuries old tradition called the running of the bulls. it began as a way to transfer bulls from the country to inside city walls, where they were either sold or used for bullfighting. the most famous bull run is in pamplona. it s part of the san fermin festival. and it has attracted tourists from all over the world since ernest hemingway popularized it in his 1926 novel, the sun also rises. but the event is not without controversy. many of the bulls who run are later killed in the bullfighting ring. animal rights groups have been calling for an end to this in spain. and it s also dangerous for the people who choose to run. cnn s david culver, went to the san fermin festival to take a a closer look k at y ththis traditionon still hols after so many centuries, and