 Complete the following phrase:  John Tzibus or Joannes Tzibus , Greek:  was a general of the Byzantine emperor Justinian I. He served as the magister militum per Armeniam, replacing the unpopular Peter. He founded the port city of Petra, Lazica, through which he monopolized the trade in Lazica, acting as a middleman. This triggered the Lazic king Gubazes II to switch sides. John Tzibus was killed by an arrow in the neck in 541 AD during the siege of his fortress by the Sasanians, who were now allied with the Lazic king. This marked the beginning of the 