Odilo, Duke of Bavaria, presides over the establishment of bishoprics in Bavaria, when in 739 Boniface establishes the dioceses of Regensburg, …

…Freising, …

…Passau, and …

Leo has repaired the extensive walls of Constantinople, and has maintained peaceful relations with the Bulgarians to the north, enabling him to concentrate his military abilities against the Arab menace to Asia Minor.

When the Caliphate invades imperial territory in 739, Leo dispatches imperial forces to engage them in Phrygia.

The Moors continue to raid Gaul, briefly occupying Arles and attacking up the valley of the Rhône River, but the Franks had halted their advance at Valence in 737 and …

…at Lyon in 739.

Leo's actions have severely strained relations with the papacy, causing the pope to turn increasingly to the Frankish kings as alternative protectors of the Holy See in Rome and weakening the imperial position in the Italian peninsula.

Leo retaliates against Gregory by halting financial contributions to the papacy from southern Italy.

The successive popes Gregory II and Gregory III have turned away from Constantinople because of increased imperial taxation, the emperor's policy of iconoclasm, and Constantinople's failure to protect Rome adequately.

Liutprand seizes four cities of the Duchy of Rome in 739.

Pope Gregory appeals to Charles Martel, the Frankish ruler of Gaul, but Charles, who had been Liutprand's ally against the Saracens in Provence, refuses aid.

Other harsh taxation and administrative measures add to Leo's unpopularity in Sicily and …

…southern Italy.

Although Leo is an able commander, he neglects to maintain strong naval forces in the western Mediterranean and thus further weakens Roman power there.

The rule in Venice of the doge Orso I ends in 739; he is succeeded by imperial officials.