The Council of Nicaea was a ecumenical conference of the early Christian church held in the Mediterranean city of Nicaea in 325 at the behest of Caesar Constantine. His goal was to try to bring order to the church that was then inflamed by a great battle between those following Alexander of Alexandria and those loyal to Arius.
The two bishops differed strongly over the issue of Jesus Christ's divinity. Alexander — represented at the council by his proxy Athanasius — felt that Christ was a different aspect of God, but God was in fact a singular being with three facets: God, Christ and the Holy Spirit. Arius, who was banned from attending the conference directly, felt that the three aspects were different entities and that God had actually created Jesus as his son.
Constantine, for his part, just wanted the matter settled so that it would stop creating civil unrest, as it had done in Alexandria and elsewhere in the Empire. Partially toward this end, he allowed the Fifth Doctor to attend to ensure things didn't get out of hand. However, the Doctor elected to take Erimem and Peri along as his clerks, and they had already met Arius. Erimem in particular was impressed with her fellow Egyptian, and took the opportunity to disobey the Doctor and speak on Arius' behalf. While she was not a Christian, and couldn't vouch for Arius' theology, she passionately believed that Arius' inability to speak in the Council was unjust.
Her behaviour got the time travellers promptly ejected from the Council, and then in trouble with the Emperor. Erimem fled from the Doctor and Peri, both of whom felt that it simply wasn't their fight. While the Council continued, she fled to Arius' secret location. News of her outburst swept through the city and support for Arius' cause grew.
Arius' sudden popularity grew into a public relations problem for Caesar Constantine. He decided that, although he had personally opened the Council, he would now personally withdraw from it, and allow the matter to be wholly settled by the bishops. Though Erimem would have preferred that Constantine would have compelled the Council to hear Arius' arguments, she at least now believed that the Emperor was no tyrant. He was not forcing the Council to simply accept the easy option.
Nevertheless, the Council did declare Arius' views heretical, embracing Alexander and Athanasius' arguments as orthodoxy.
Because of its wide-ranging, long-lasting impact on the Christian church, the Fifth Doctor characterised the Council of Nicaea as what later incarnations would call a "fixed point in time". He believed Athanasius' victory to be immutable. (AUDIO: The Council of Nicaea)