First the authorities locked her in a hot sauna for three days
to try and suffocate her. That did not kill her. Next, they
attempted to behead her three times, the maximum legal limit, but
were unable to sever her head. After 3 days suffering from a mortal
wound she did die.
St. Cecilia was arrested for being a Christian and sentenced to death, but since she was a noble it was to be a private death. Her captures locked her in her bath to suffocate her. When this failed an executer was sent in to behead her. He was unnerved however and after three bows to her neck he failed to cut off her head. Three blows where what was perscribed by law at the time. The executioner fled and left her to die. She stayed alive praying for three days. She was buried and later found incorrupt. (Her body hadn't decomposed) Her body is the first known case of this phenomenon.