Why was Mark the Evangelist martyred?

A:The apocryphal 'Acts of Mark' say that the residents of Alexandria sought to martyr the apostle because he formed the Christian community in this city. It says that he was dragged through the streets of Alexandria until dead.

Of course, we can not pick and choose when it comes to apocryphal works. Either the Acts of Mark is a true and historical account of the early Church and should be accorded a status alongside Acts of the Apostles, or the entire book should be read with suspicion. As with all the early apostles, we have no genuine evidence that he was ever martyred, and no good reason to accept this story.

We do not know that Mark was really martyred or, if so, why.