 The church had an ancient origin : during the Middle Ages it was dedicated to the Redeemer ( Italian : Salvatore ) , and was called San Salvatoris de Coxa Caballi in the papal bulls of Sergius I ( r . 687 – 701 ) and Leo IV ( r . 847 @-@ 55 ) . It is also mentioned in the main medieval catalogues of Roman churches , like that of Cencio Camerarius and of Paris . 
