Final answer:
Pope Alexander died from pneumonia, a common illness at the time that was fatal since there were no effective treatments available.
Step-by-step explanation:
Pope Alexander's death was due to natural causes. He died from pneumonia, which was a common illness at the time. Medical science had not advanced to the point where it could effectively treat pneumonia, so it was a fatal condition in those days. If he had lived in a later time period, there may have been better treatment options available that could have saved his life.