Between two councils: AD 325-381

During the lifetime of those who gather at Nicaea in AD 325 Arianism remains a controversial issue. Before the end of Constantine's reign Arius himself is brought back from exile. By mid-century, under Constantius (one of Constantine's sons), Arianism is actively favoured, with most of the influential positions in the church held by Arian bishops.

Over the years new middle ways are explored. Some suggest that the Son is 'of similar substance' (homoi-ousios) to the Father; others that he is 'like' Him (homoios). But eventually the debate runs out of steam - particularly when a pagan emperor, Julian the apostate, concentrates the minds of the Christians by dismissing all their notions.

By AD 381, with a new generation of bishops and a new emperor, Theodosius, who is anti-Arian, the council summoned to Constantinople is in no mood for compromise. It conclusively rejects the Arian heresy and formally adopts a slightly modified version of the statement of faith promulgated at Nicaea. This AD 381 version is the text which becomes known as the Nicene creed.

And there the matter would seem, at first sight, to have ended. But it transpires that Arianism, like an irrepressible virus, has already spread elsewhere. The carrier is a remarkable man, Ulfilas, who in about 340 is appointed bishop to the barbarian Goths settled north of the Danube.

Ulfilas is the first man known to have undertaken an extraordinarily difficult intellectual task - writing down, from scratch, a language which is as yet purely oral. He even devises a new alphabet to capture accurately the sounds of spoken Gothic, using a total of twenty-seven letters adapted from examples in the Greek and Roman alphabets.

God's work is Ulfilas' purpose. He needs the alphabet for his translation of the Bible from Greek into the language of the Goths. It is not known how much he completes, but large sections of the Gospels and the Epistles survive in his version - dating from several years before Jerome begins work on his Latin text.

Unfortunately for the cause of orthodoxy, the ministry of Ulfilas falls in the period when Arianism has its strongest following. Ulfilas himself subscribes to one of the milder versions, that which says Jesus is 'like' his Father. In this account the Trinity contains an element of hierarchy, with Jesus slightly below God and the Holy Spirit trailing both. It makes sense to the Goths, though most remain pagan till long after Ulfilas' death.

The Arian faith eventually becomes something of a national creed for the Germanic tribes. It is adopted, from the Goths, by the Vandals and by many other groups. And with the Germanic tribes on the move, in the upheavals of the 5th century, so Arianism spreads.

At various times in the 5th and 6th centuries, Italy is largely Arian under the Ostrogoths; Spain is Arian under the Visigoths; and north Africa is Arian under the Vandals.

The heresy is eliminated in most of these areas by the energetic campaigning of an orthodox emperor in Constantinople, Justinian. But another barbarian group, the Lombards, bring it back to north Italy in the late 6th century. In Visigothic Spain an Arian king is converted to orthodoxy in the 6th century and actively persecutes Arians from 589, but traces of the heresy remain until after the Muslims conquer in 711. By then the story has run for four centuries. Constantine, at Nicaea in 325, would not have approved.