According to Wikipedia, the festival commemorates both the birthday of Murugan (alsoSubramaniam), the youngest son of god Shiva and his wifeParvati, and the occasion when Parvati gave Murugan a vel(spear) so he could vanquish the evil demon Soorapadman. To me, it is a form of ritual art which is to test the human spirit to carry kavadi (such as below) to re-pay the idol god for averting great calamity in their lives.
