Daniel L. Schwartz (eds.), "The Letters of Severus of Antioch" in last modified February 2, 2018, http://syriaca.org/work/10541
    
        
            
               The Letters of Severus of Antioch
               
                    
                        Severus
                        of Antioch
                        
                     — 
                       ܣܘܝܪܝܘܣ
                       ܕܐܢܛܝܘܟܝܐ
                     
               
                
                    This Greek collection of the Letters of 
                    Severus 
                    is no longer extant. The collection contained at least 3824 letters in 23 books organized according to when they were written. 
                    The first section contained letters from before the episcopacy (books 1-4), 
                    the second letters from during the episcopacy (books 5-14), 
                    and the third letters from after Severus' expulsion (books 15-23). 
                    A smaller collection of these letters also circulated in Greek under the title, 
                    The Select Letters of 
                        Severus of Antioch
           . 
                    This collection, which numbered at least 700 letters, is also no longer extant. 
                    However, 123 letters from this smaller collection is extant in Syriac translation in 
                    The Sixth Book of the Select Letters of 
                        Severus of Antioch
           , 
                    edited and translated by E. W. Brooks. Additional letters from this collection and some from outside of it are also extant.
                
                http://syriaca.org/work/10541
                
                
                    The Sixth Book of the Select Letters of Severus Patriarch of Antioch, vol. 2.1
                   
                
                
                    A Collection of Letters of Severus of Antioch from Numberous Manuscripts