Many theological discussions on the Trinity were organized in 1568, the first of them taking place in his presence in Gyulafehérvár from 8 to 17 March. The growing influence of the Anti-Trinitarians on John Sigismund became obvious in 1569. After Péter Károlyi, a Calvinist cleric, complained about John Sigismund's bias, John Sigismund accused the Calvinist bishop, Melius, of having persecuted non-Calvinist priests, stating that Melius "should not play the pope". The largest debate between the Calvinist and Anti-Trinitarian, or Unitarian, theologians took place in Nagyvárad from 20 to 25 October 1569. Although neither side was declared winner, after the debate John Sigismund accepted Anti-Trinitarian ideas, which made him the only Unitarian monarch in history.