According to John Meyendorff,[110] and John Romanides[111] the Western efforts to get Pope Leo III to approve the addition of Filioque to the Creed were due to a desire of Charlemagne, who in 800 had been crowned in Rome as Emperor, to find grounds for accusations of heresy against the East. The Pope's refusal to approve the interpolation avoided arousing a conflict between East and West about this matter. Emperor Charlemagne accused the Patriarch of Constantinople (Saint Tarasios of Constantinople) of infidelity to the faith of the First Council of Nicaea, because he had not professed the procession of the Holy Spirit from the Father "and the Son", but only "through the Son", an accusation strongly rejected by Rome, but repeated in Charlemagne's commissioned work the Libri Carolini, books also rejected by the Pope.[112] Pope Leo rejected the request of Charlemagne's emissaries for approval of inclusion of the Filioque in the Latin Creed used in Rome. So, during the time of Pope Leo's leadership, 795-816, and for another two centuries, there was no Creed at all in the Roman rite Mass.

Although he approved the Filioque doctrine,[32][107][113][114] Pope Leo III in 810 opposed adding the Filioque to the Creed,[107] and had two heavy silver shields made and displayed in St Peter's, containing the original text of the Creed of 381 in both Greek and Latin,[32] adding: "I, Leo, have placed these for love and protection of the orthodox faith".[115]