The Arsenite Schism was a schism within the Church of Constantinople that resulted from the refusal of Patriarch Arsenius to remove the sentence of excommunication from Michael VIII Palaiologos for his blinding of the child emperor John IV Laskaris in 1261.
Michael Palaiologos, with a distinguished genealogy among the aristocracy of Constantinople, became the joint guardian for the eight-year old emperor John IV Doukas Laskaris together with Patriarch Arsenius following a coup in 1258, after the death of emperor Theodore II Doukas Laskaris. On January 1, 1259, Michael was proclaimed co-emperor as Michael VIII Palaiologos.
After the capture of Constantinople from the last Latin emperor, Baldwin II, on July 25, 1261, Michael VIII returned to Constantinople on August 15 from Nicea without the young co-emperor John IV. There, he was crowned emperor with his son Andronikos II Palaiologos as co-emperor. In December 1261, Michael VIII had John IV blinded so that he was no longer eligible to be emperor and, then, had him sent to a monastery.
For this act, Patr. Arsenius excommunicated Michael VIII. Unable to reconcile their differences, emperor Michael deposed Patr. Arsenius, in 1265, and exiled him to Prokonessos in the Sea of Marmara. Arsenius' deposition was the start of the "arsenite schism". To replace Arsenius, Michael appointed Germanus patriarch as Germanus III. Patr. Arsenius was well connected with supporters in the monastic community in addition to those that supported the Laskarid dynasty. The supporters of Patr. Arsenius strongly opposed the uncanonical appointment of Germanus. Their opposition resulted in him submitting his resignation as patriarch in 1266.
After Patr. Germanus' resignation, emperor Michael VIII appointed his confessor, Joseph, as Germanus' successor in 1267. Patr. Joseph I quickly absolved emperor Michael of blinding John Laskaris and lifted the excommunication imposed by Patr. Arsenius.
Supporters of Patr. Arsenius strongly rejected and opposed Patriarch Joseph and the Emperor, creating a split between the Arsenites and the imperial patriarchate. Their actions were based on personal loyalty as well as the canon law of the Church. This schism was exacerbated by the support given by emperor Michael and Patr. Joseph toward a union of East with the West at the Second Council of Lyons, which was seen as a further betrayal of Orthodoxy. The schism between the Arsenites and the imperial Church lasted until 1310, a period of 45 years after Arsenius' deposition and 16 years after his death. The reconciliation was concluded during the patriarchate of Patr. Nephon I, which finally ended the schism.