text: And then there is such thing as 'oral tradition'. An increasing number of historians claim that on average, oral tradition is not more or less reliable than written tradition. 
  
  Christian tradition involves both, written and oral or living tradition. As far as the oral tradition of Mark's martyrdom and veneration of his remains at the Martyrium of Mark goes, they certainly predate 313 AD, when any of such claim or practice would have been more of a liability than a desirable asset. 
  
  When you have a consistent oral (living) tradition that involves continuous practice, especially when originating under difficult circumstances, you cannot simply dismiss it as "legend." It is a credible-enough evidence and, as such, its falsity requires actual proof to the contrary.