On Monday 23 May 550 a directive was issued by the Emperor Justinian to John, metropolitan bishop of Anazarbus in Cilicia Secunda. Another directive, cast in corresponding terms, was sent to Cosmas, bishop of Mopsuestia (the present day Misis, seventeen miles east of Adana in southern Turkey) in the same province. ‘We indicate to your holiness”, he writes to John, ‘that you are to convene all the most-religious bishops of your synod; you are to repair to the town of Mopsuestia and make a detailed examination, with the senior men (whether clerics or laity), there established, foregathering, and learn from them whether they know the date when Theodore's name was removed from the diptychs.” If the senior persons in question do not know the answer, the fact is to be expressly recorded and the diptychs themselves are to be duly checked. Into the events leading up to this directive I will not now enter. It must suffice to recall that the setting was the so-called Three Chapters Controversy: what to do about Nestorius' precursors Theodore and Diodore, about Theodoret's writings against Cyril of Alexandria's twelve Anathematisms and the Letter of Ibas to Maris. On these matters the Council of Chalcedon had been indecisive. A hundred years after that council, it looked to many people, the emperor included, as if a few modest addenda to the council's decisions, amounting, perhaps, to nothing more than explications of its mind on Nestorius and his school, would put an end to the painful disunity of eastern Christendom.