The theology of the Holy Spirit waited through the early Christian centuries until the main doctrines regarding the Trinity and the person of Christ had been forged. Even then pneumatology was introduced ‘by the back door’, in Theodore Campbell's phrase, that of how the Son was placed in the Father, Son and Spirit confession. While prayers to the Spirit were not lacking in the earliest liturgies, still, at Nicea the doctrine ‘had been disposed of in lapidary brevity’, as Jaroslav Pelikan has described the credal line, ‘and we believe in the Holy Spirit’. ‘Nor does there seem to have been a single treatise dealing specifically with the person of the Spirit composed before the second half of the fourth century’. After Nicea, however, controversy concerning the Spirit erupted ‘with a vengeance’, producing the same kind of energy that had accompanied the Christological debates. Pneumatomachi, Tropici, and Macedonians, though losers in the fight for orthodox doctrine on the Spirit's nature, had mounted formidable campaigns, as Arians had done over the relationship of Christ to the Father. But disagreement over the Spirit had an even greater impact than Arian opposition in that the filioque remains a principal difference between the Catholic and Orthodox, and now Catholic and Anglican, creeds.