He played other prominent roles in diplomatic affairs as "mesazon" to the two emperors. He was a witness to John's treaties with the Republic of Venice in September 1423, May 1431, October 1436, September 1442, and July 1447. He also played a heroic part in the final defense of Constantinople; according to Donald Nicol, he commanded a unit of 700 men stationed in the neighborhood of the Church of the Holy Apostles with his son-in-law Nikephoros Palaiologos, while Steven Runciman assigns him to a command of a portion of the Theodosian Walls next to the Sea of Marmora.