Leo III (died June 12, 816) was Pope from 795 to 816.

Leo announced his election to Charlemagne, sending him the keys of Saint Peter's tomb and the banner of Rome, requesting an envoy. Charlemagne in his reply stated that it was his function to defend the church and the Pope's to pray for the realm and for victory of the army.

Leo, coming from a common-folk background, aroused the hostility of the Rome's nobility, who saw the papal post as reserved for noble candidates. In April 799 he was attacked by a gang, who attempted to gouge out his eyes and cut off his tongue. He was then formally deposed and sent to a monastery, but escaped and made his way to Charlemagne, who did not recognise the deposition. The opposition in Rome sent representatives to Charlemagne to present their case. Alcuin, Charlemagne's adviser, pointed out that no earthly power could judge the Pope, and so Leo was escorted back to Rome.

Charlemagne went to Rome in November 800, and on December 1 held a council

Leo helped restore King Eardulf of Northumbria, and settled various matters of dispute between the Archbishops of York and Canterbury. He also reversed the decision of his predecesor in regards to the granting of the pallium to the bishop of Lichfield, Higbert. He believed that the English episcopate had been misrepresented before Hadrian and that therefore his act was invalid. In 803, Lichfield was a regular diocese again.

The reasons for the coronation, the involvement beforehand of the Frankish court, and the relationship to the Byzantine Empire are all matters of debate among historians. An effective administrator of the papal territories, Leo contributed to the beautification of Rome.

His feast day, formerly, was June 12.

Лъв III (папа) Leo III. (Papst) León III (Papa) Léon III (pape) 교황 레오 3세 Papa Leone III Paus Leo III III. Leó pápa Paus Leo III レオ3世 (ローマ教皇) Papież Leon III Papa Leão III Pyhä Leo III Leo III (påve) 良三世 (教宗)