Nicholas I Patriarch of Constantinople.
Letters /
Nicholas I, Patriarch of Constantinople ; Greek text and English translation by R.J.H. Jenkins, L.G. Westerink 
. - Washington : Dumbarton Oaks,  Center for Byzantine Studies,  Trustees for Harvard University,  1973 
. - XL, 631 p.  24 cm. 
 - Corpus fontium historiae Byzantinae  v. 6 .
<br/><label>  ISBN: </label>0-88402-039-8