Summoned by Pope Pius IX by the bull Aeterni Patris of 29 June 1868. The first session was held in St Peters basilica on 8 December 1869. It was the 20th ecumenical council of the Roman Catholic church. Nearly 800 church leaders attended.
The pope's primary purpose was to obtain confirmation of the position he had taken in his Syllabus of Errors (1864), condemning a wide range of positions associated with rationalism, liberalism, and materialism.
The purpose of the council was, besides the condemnation, to define the doctrine concerning the church. In the three sessions, there was discussion and approval of only two constitutions: Dogmatic Constitution On The Catholic Faith and First Dogmatic Constitution on the Church of Christ, the latter dealing with the primacy and papal infallibility of the bishop of Rome - whether when a pope speaks ex cathedra on faith or morals he does so with supreme apostolic authority (that which no Catholic may question or reject). About 60 members of the council effectively abstained by leaving Rome the day before the vote and the debate was still heated, Bishop (later canonized) Antonio Maria Claret suffered a fatal heart-attack during the debate shortly after condemining the "blasphemies and heresies uttered on the floor of this Council". The discussion and approval of the constitution gave rise to serious controversies which led to the withdrawal from the church of those known as Old Catholics.
The outbreak of the Franco-Prussian War interrupted the council. It was suspended following the capture of Rome and never resumed, nor was it ever officially closed. The results of the council marked the triumph of the Ultramontanism movement.
see also Ecumenical council