10. The Second Council of the Lateran, 1139 A.D.

The Second Council of the Lateran was the tenth ecumenical council recognized by the Catholic Church. It was convened by Pope Innocent II in April 1139 and attended by close to a thousand clerics. Its immediate task was to neutralise the after-effects of the schism which had arisen after the death of Pope Honorius II in 1130 and the papal election that year that established Pietro Pierleoni as the antipope Anacletus II.