Why does Saint Paul have a sword in pictures of him?

Two possible explanations: 1) The sWord is "the sWord of the Spirit, which is the Word of God." (Eph. 3:17). 2) More likely (IMHO) though, it is likely meant to mirror the upside down cross of Peter, both representing the means by which each was martyred. Both explanations are cited in the Westminster Cathedral tour of the Chapel of St. Paul (http://www.westminstercathedral.org.uk/art/art_chspaul.html). A third explanation: According to legend he died by the sWord. In Legend, Paul is arrested by the Roman emperor Nero and is sentenced to death by the sWord, because he was a Roman citizen. Otherwise he would have been crucified.