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According to the Catholic Church, a Church Council is ecumenical ("world-wide"), if it is "a solemn congregation of the Catholic bishops of the world at the invitation of the Pope to decide on matters of the Church with him". 
In addition to ecumenical Councils, there are “particular Councils”. Current Canon Law recognizes two kinds of particular Councils: plenary councils involve the bishops of an episcopal conference (usually a single country)  and provincial councils the bishops of an ecclesiastical province. 
The Catholic Church recognizes as ecumenical 21 councils occurring over a period of some 1900 years.   The ecumenical nature of some Councils was disputed for some time, but was eventually accepted, for example the First Lateran Council and the Council of Basel. A 1539 book on ecumenical councils by Cardinal Dominicus Jacobazzi excluded them, as did other scholars. 
The first few centuries did not know large-scale councils; they were feasible only after the Church had gained freedom from persecution under Emperor Constantine. As a result, the Council of Jerusalem or Apostolic Council, held in Jerusalem around AD 50 and described in Acts of the Apostles chapter 15, is not an ecumenical Council, even though most Christian denominations consider that it expresses a key part of Christian doctrine and moral teaching.
These comprised the hierarchs of the undivided Church (i.e. both East and West), and are accepted as authoritative, not only by Catholics, but also by the Eastern Orthodox Church and many Protestant denominations.
The First Council of Nicaea (May 20 – July 25?, 325) formulated the original Nicene Creed. Most importantly, the council defined the equality of God the Father and Christ, his son. It taught that Jesus was of the same substance as God the Father and not just merely similar.  By defining the nature of the divinity of Jesus, the council did not solely rely on the Bible but jointly gave it a binding interpretation. The council issued 20 canons  and repudiated Arianism.
The First Council of Constantinople defined in four canons the Nicene Creed, which is still used in the Catholic Church. Most importantly, it defined the divinity of the Holy Spirit, which is derived from Apostolic Tradition but not defined in the Bible. The council met from May until July 381 during the pontificate of Pope Damasus I and issued four canons.
The Council of Ephesus proclaimed the Virgin Mary as the Theotokos (Greek Η Θεοτόκος, "Mother of God" or "God-bearer"). The council met in seven sessions during the pontificate of Pope Celestine I from June 22 until July 17, 431. It rejected Nestorianism.
The Council of Chalcedon defined the two natures (divine and human) of Jesus Christ. "We teach unanimously that the one son, our lord Jesus Christ to be fully God and fully human."  It met in 17 sessions from October 8 until November 451 during the pontificate of Pope Leo the Great. It issued 28 canons, the last one defining equality of the bishops of Rome and Constantinople, which was rejected by the papal delegates and Pope Leo the Great. 
The first three of these are recognized as ecumenical by both Catholics and Orthodox, but the fourth is not accepted by the Eastern Orthodox Church.
The council again dealt with the issue of the two natures of Christ, as monophysitism had spread through Christianity despite the decisions of Chalcedon. The council met from May 5 until June 2, 553, in eight sessions during the pontificate of Pope Vigilius, who was imprisoned during the council by the emperor.  It condemned "Three Chapters" of Nestorian writings. Several Catholic provinces refused to accept the Second Council of Constantinople because of the political pressures. 
The council repudiated Monothelitism, and reaffirmed that Christ, being both human and divine, had both human and divine wills. It met in sixteen sessions from November 7, 680, until September 16, 681. The council was held during the pontificates of Pope Agatho and Pope Leo II. It also discussed the views of Honorius.
In 730, the emperor outlawed pictorial presentations of Christ and the saints and created thus. These comprised the hierarchs of the undivided Church (i.e. both East and West), and are accepted, not only by Catholics, but also by the Eastern Orthodox Church and many Protestant denominations. The first iconoclasm. The Pope argued against it and convened in 731 a local council in Rome to no avail.  The council discussed and restored the veneration of icons using the Bible and tradition of the Church as arguments. Pictures of Christ, the Blessed Virgin Mary and the Saints were used to stimulate piety and imitation. The council met in eight sessions from September 24, 787, until October 23, 787, during the pontificate of Pope Hadrian I. It issued twenty canons.  This was the last ecumenical council to be accepted by both Eastern and Western churches.
With the coronation of Charlemagne by Pope Leo III in 800, his new title as Patricius Romanorum, and the handing over of the keys to the Tomb of Saint Peter, the papacy had acquired a new protector in the West. This freed the pontiffs to some degree from the power of the emperor in Constantinople, but it also led to a schism, because the emperors and patriarchs of Constantinople interpreted themselves as the true descendants of the Roman Empire dating back to the beginnings of the Church.  Pope Nicholas I had refused to recognize Patriarch Photios I of Constantinople, who in turn had attacked the pope as a heretic, because he kept the filioque in the creed, which referred to the Holy Spirit emanating from God the Father and the Son. The council condemned Photius, who questioned the legality of the papal delegates presiding over the council, and ended the schism.  The council met in ten sessions from October 869 to February 870 and issued 27 canons.
All of these councils took place in the West and were attended by Western bishops.
Successors of Charlemagne insisted increasingly on the right to appoint bishops on their own, which led to the Investiture Controversy with the popes. The Concordat of Worms signed by Pope Calixtus II included a compromise between the two parties, by which the pope alone appoints bishops as spiritual head while the emperor maintains a right to give secular offices and honors. Pope Calixtus invoked the council to ratify this historic agreement.  There are few documents and protocols left from the sessions and 25 canons approved. The council met from March 18 to April 5, 1123.
After the death of Pope Honorius II (1124–1130), two popes were elected by two groups of cardinals. Sixteen cardinals elected Pope Innocent II, while others elected Antipope Anacletus II who was called the Pope of the Ghetto, in light of his Jewish origins.  The council deposed the antipope and his followers. In important decisions regarding the celibacy of Catholic priests, clerical marriages of priests and monks, which up to 1139 were considered illegal, were defined and declared as non-existing and invalid. The council met under Pope Innocent II in April 1139 and issued 30 canons.
The council established the two-thirds majority necessary for the election of a pope. This two-thirds majority existed until Pope John Paul II. His change was reverted to the old two-thirds majority by Pope Benedict XVI in his Moto Proprio, De Aliquibus Mutationibus, from June 11, 2007. Still valid today are the regulations that outlawed simony, and the elevation to Episcopal offices for anyone under thirty. The council also ruled it illegal to sell arms or goods which could assist armaments to Muslim powers. Saracens and Jews were forbidden from keeping Christian slaves.  All cathedrals were to appoint teachers for indigent and low-income children. Catharism was condemned as a heresy. This council is well documented: Reports include the saga of an Irish bishop whose income consisted in the milk from three cows. If one of the cows would stop giving milk, the faithful were obliged to donate another animal.  The council met in March 1179 in three sessions and issued 27 chapters, which were all approved by Pope Alexander III.
The council mandated every Christian in serious sin is to go at least once a year on Easter to confession and to receive the Holy Eucharist. The council formally repeated Catholic teaching, that Christ is present in the Eucharist and thus clarified transubstantiation. It dealt with several heresies without naming names but intended to include the Catharists and several individual Catholic theologians. It made several political rulings as well.  It met in only three sessions in November 1215 under Pope Innocent III and issued 70 chapters.
The council continued the political rulings of the previous council by deposing Frederick II, as German king and as emperor. Frederick was accused of heresy, treason and arresting a ship with about 100 prelates willing to attend a meeting with the pope. Frederick outlawed attendance at the council and blocked access to Lyon from Germany. Therefore, the majority of council fathers originated from Spain, France and Italy. The council met in three sessions from June 28, 1245, and issued 22 chapters all approved by Pope Innocent IV.
Pope Gregory X defined three aims for the council: aid to Jerusalem, union with the Greek Orthodox Church and reform of the Catholic Church. The council achieved a short-lived unity with the Greek representatives, who were denounced for this back home by the hierarchy and the emperor. A teaching on purgatory was defined. Papal conclaves were regulated in Ubi periculum, which specified that electors must be locked up during the conclave and, if they could not agree on a pope after eight days, would receive water and bread only. Franciscan, Dominican, and other orders had become controversial in light of their increasing popularity. The council confirmed their privileges. Pope Gregory X approved all 31 chapters, after modifying some of them, thus clearly indicating papal prerogatives. The council met in six sessions from May 7 to July 17, 1274, under his leadership.
Pope Clement V solemnly opened the council with a liturgy, which has been repeated since in all Catholic ecumenical councils. He entered the Cathedral in liturgical vestments with a small procession and took his place on the papal throne. Patriarchs, followed by cardinals, archbishops and bishops, were the next in rank. The Pope gave a blessing to the choir, which intoned the Veni Sancte Spiritus.  The Pope issued a prayer to the Holy Spirit, the litany of saints was recited and only after additional prayer did the Pope actually address the council and open it formally. He mentioned four topics, the Order of Knights Templar, the regaining of the Holy Land, a reform of public morality and freedom for the Church. Pope Clement had asked the bishops to list all their problems with the order. The Templars had become an obstacle to many bishops because they could act independently of them in such vital areas as filling parishes and other positions. Many accusations against the order were not accepted as the Pope ruled that confessions under torture were inadmissible. He withdrew canonical support for the order but refused to turn over its properties to the French king.  The council fathers discussed another crusade, but were convinced instead by Raimundus Lullus that knowledge of foreign languages is the only way to Christianize Muslims and Jews. He successfully proposed the teaching of Greek, Hebrew, and Arabic languages in Catholic universities.  With this the council is considered to have begun modern missionary policies. In the three sessions, the council discussed further Franciscan poverty ideals. It met from October 1311 until May 1312.
All of these councils were called to reform the Church. The first three were involved in an ongoing debate about over the alleged superiority of an ecumenical council over the pope.
Before the council there was the Western Schism, with three popes each claiming legitimacy. One of them, John XXIII, called for the council to take place in Constance (Konstanz), Germany, hoping it would secure him additional legitimacy. When opinion in the council moved against him in March 1415, he fled to Schaffhausen  and went into hiding in several Black Forest villages such as Saig.
After his flight, the council issued the famous declaration Sacrosancta, which declared that popes are below, not above, an ecumenical council. The council deposed all three popes and installed Pope Martin V,  who made his peace with John XXIII by installing him as a cardinal. It also provided for future councils to be held, and signed five concordats with the major participating nations.
Reforms did not materialize as hoped for, because the reformers disagreed among themselves. John Hus, a Bohemian reformer, was issued an imperial guarantee for safe conduct to and from the council. However, after he contravened the agreement by saying Mass and preaching in public, he was arrested, tried for heresy, and burned at the stake by the civil authorities in 1415. 
The Council of Constance was one of the longest in Church history, meeting in 45 sessions from November 4, 1414, until April 22, 1418. The influx of 15,000 to 20,000 persons into the medieval city of 10,000 created dramatic monetary inflation: the German poet Oswald von Wolkenstein wrote, "Just thinking of Constance, my purse begins to hurt." 
The council continued debate on conciliarism. The papal delegate opened the council in Basel on July 23, 1431, without a single bishop present. When he tried to close it later, bishops insisted on citing the pope to the council, which he refused. The council continued on its own and issued several decrees on Church reform. Most of the participants were theologians; bishops made only ten percent of the eligible voters. The Pope moved the council to Ferrara, where he achieved a major success, when the Greek Orthodox Church agreed to unity with Rome. But conciliarism continued to be the politically correct trend, as "reform" and "council" were seen as inseparable.  Formally, the Council of Basel was never closed. The council decreed in 1439 (a short-lived) union with Greek, Armenian, and Jacobite Churches (1442). The council had 25 sessions from July 1431 until April 1442. It met under Pope Eugene IV in Basel, Germany, and Ferrara and Florence Italy. It was moved to Rome in 1442.
The Fifth Council of the Lateran opened under the leadership of the Pope in Rome. It taught that the soul of a human being lives forever (but see the current understanding of eternal life  ). As previous councils, it condemned heresies stating the opposite without mentioning names. The opening sermon included the sentence: "People must be transformed by holiness not holiness by the people."  The issue was reform and numerous small reforms were approved by the council, such as selection of bishops, taxation issues, religious education, training of priests, improved sermons, etc., but the larger issues were not covered and Pope Leo X was not particularly reform-minded. The council condemned as illegal a previous meeting in Pisa.  The council met from 1512–1517 in twelve sessions under Pope Julius II and his successor Pope Leo X.  This was the first council to have a representative from the New World, Alessandro Geraldini, the Archbishop of Santo Domingo, attend. 
The council issued condemnations on what it defined as Protestant heresies and it defined Church teachings in the areas of Scripture and Tradition, Original Sin, Justification, Sacraments, the Eucharist in Holy Mass and the veneration of saints. It issued numerous reform decrees.  By specifying Catholic doctrine on salvation, the sacraments, and the Biblical canon, the council was answering Protestant disputes.  The council entrusted to the pope the implementation of its work, as a result of which Pope Pius V issued in 1566 the Roman Catechism, in 1568 a revised Roman Breviary, and in 1570 a revised Roman Missal, thus initiating the Tridentine Mass (from Trent's Latin name Tridentum), and Pope Clement VIII issued in 1592 a revised edition of the Vulgate.
The Council of Trent is considered one of the most successful councils in the history of the Catholic Church, firming up Catholic belief as understood at the time. It convened in Trent between December 13, 1545, and December 4, 1563, in twenty-five sessions for three periods. Council fathers met for the 1st–8th sessions in Trent (1545–1547) and for the 9th–11th sessions in Bologna (1547) during the pontificate of Pope Paul III.  Under Pope Julius III, the council met in Trent (1551–1552) for the 12th–16th sessions. Under Pope Pius IV the 17th–25th sessions took place in Trent (1559–1565).
The council, also known as Vatican I, was convened by Pope Pius IX in 1869 and had to be prematurely interrupted in 1870 because of advancing Italian troops. In the short time, it issued definitions of the Catholic faith, the papacy and papal infallibility. Many issues remained incomplete, such as a definition of the Church and the authority of the bishops. Many French Catholics desired the dogmatization of Papal infallibility and the assumption of Mary in the ecumenical council. 
Nine mariological petitions favoured a possible assumption dogma, which however was strongly opposed by some council fathers, especially from Germany. On May 8, the fathers rejected a dogmatization at that time, a decision shared by Pope Pius IX. The concept of co-redemptrix was also discussed but left open. In its support, council fathers highlighted the divine motherhood of Mary and called her the mother of all graces.  But by the time of Vatican II it was passed over for reasons given  and later avoided because of its ambiguity. The council met in four sessions from December 8, 1869, to July 18, 1870. 
The Second Vatican Council, also known as Vatican II, was convoked by Pope John XXIII and met from 1962 to 1965. Unlike most previous councils, it did not issue any condemnations, as its objective was pastoral. But it issued 16 magisterial documents: 
The general sessions of the council were held in the autumns of four successive years (in four periods) 1962 through 1965. During the other parts of the year special commissions met to review and collate the work of the bishops and to prepare for the next session. Sessions were held in Latin in St. Peter's Basilica, with secrecy kept as to discussions held and opinions expressed. Speeches (called interventions) were limited to ten minutes. Much of the work of the council, though, went on in a variety of other commission meetings (which could be held in other languages), as well as diverse informal meetings and social contacts outside of the council proper.
Those eligible for seats at the council were 2,908 men, referred to as council fathers, including all bishops around the world, as well as many superiors of male religious orders. In the opening session 2,540 took part, making it the largest gathering in any council in church history. (This contrasts with Vatican I, where 737 attended, mostly from Europe.)  Attendance varied in later sessions from 2,100 to over 2,300. In addition, a varying number of periti (Latin for "experts") were available for theological consultation—a group that exercised a major influence as the council went forward. Seventeen Orthodox Churches and Protestant denominations sent observers.  More than three dozen representatives of other Christian communities were present at the opening session, and the number grew to nearly a hundred by the end of the 4th council session.
The rules and practices concerning ecumenical Councils have varied over the centuries. Many of the earlier Councils were not subject to the rules currently in force, but were accepted as ecumenical by the practice of the time.  Today an ecumenical council can be convoked only by the Pope,  but the first 8 councils (from the 4th to the 9th century) were convoked by the Christian Roman Emperor. Bishops are always the primary participants at councils,  but a variety of other people have attended different Councils: for instance 800 abbots – outnumbering the bishops -- and some secular rulers took part in the Fourth Lateran Council (1215). Today, the Pope decides on the matters to be discussed and the procedure to be followed at an ecumenical council,  but at all councils except the last two (Vatican I and II), these were decided by the assembled bishops.
These are the provisions of the 1983 Code of Canon Law concerning ecumenical councils:
The Council of Trent, held between 1545 and 1563 in Trent, now in northern Italy, was the 19th ecumenical council of the Catholic Church. Prompted by the Protestant Reformation, it has been described as the embodiment of the Counter-Reformation.
An ecumenical council, also called general council, is a meeting of bishops and other church authorities to consider and rule on questions of Christian doctrine, administration, discipline, and other matters in which those entitled to vote are convoked from the whole world (oikoumene) and which secures the approbation of the whole Church.
The First Ecumenical Council of the Vatican, commonly known as the First Vatican Council or Vatican I was convoked by Pope Pius IX on 29 June 1868, after a period of planning and preparation that began on 6 December 1864. This was the 20th ecumenical council of the Catholic Church, held three centuries after the Council of Trent, opened on 8 December 1869 and was adjourned on 20 October 1870 after the Capture of Rome. Unlike the five earlier general councils held in Rome, which met in the Lateran Basilica and are known as Lateran councils, it met in Saint Peter's Basilica in the Vatican, hence its name. Its best-known decision is its definition of papal infallibility.
The pope, also known as supreme pontiff, Roman pontiff or sovereign pontiff, is the bishop of Rome, head of the worldwide Catholic Church, and has also served as the head of state or sovereign of the Papal States and later the Vatican City State since the eighth century. From a Catholic viewpoint, the primacy of the bishop of Rome is largely derived from his role as the apostolic successor to Saint Peter, to whom primacy was conferred by Jesus, who gave Peter the Keys of Heaven and the powers of "binding and loosing", naming him as the "rock" upon which the Church would be built. The current pope is Francis, who was elected on 13 March 2013.
Pope Paul VI was head of the Catholic Church and sovereign of the Vatican City State from 21 June 1963 to his death in August 1978. Succeeding John XXIII, he continued the Second Vatican Council, which he closed in 1965, implementing its numerous reforms. He fostered improved ecumenical relations with Eastern Orthodox and Protestant churches, which resulted in many historic meetings and agreements.
A synod is a council of a Christian denomination, usually convened to decide an issue of doctrine, administration or application. The word synod comes from the Greek: σύνοδος [ˈsinoðos] meaning "assembly" or "meeting" and is analogous with the Latin word concilium meaning "council". Originally, synods were meetings of bishops, and the word is still used in that sense in Catholicism, Oriental Orthodoxy and Eastern Orthodoxy. In modern usage, the word often refers to the governing body of a particular church, whether its members are meeting or not. It is also sometimes used to refer to a church that is governed by a synod.
Pope Vitalian was the bishop of Rome from 30 July 657 to his death. His pontificate was marked by the dispute between the papacy and the imperial government in Constantinople over Monothelitism, which Rome condemned. Vitalian tried to resolve the dispute and had a conciliatory relationship with Emperor Constans II, who visited him in Rome and gave him gifts. Vitalian's pontificate also saw the secession of the Archbishopric of Ravenna from the papal authority.
The College of Cardinals, or more formally the Sacred College of Cardinals, is the body of all cardinals of the Catholic Church. As of 10 January 2023, its current membership is 223, of whom 125 are eligible to vote in a conclave to elect a new pope. Cardinals are appointed by the pope for life. Changes in life expectancy partly account for the increases in the size of the college.
The magisterium of the Roman Catholic Church is the church's authority or office to give authentic interpretation of the Word of God, "whether in its written form or in the form of Tradition." According to the 1992 Catechism of the Catholic Church, the task of interpretation is vested uniquely in the Pope and the bishops, though the concept has a complex history of development. Scripture and Tradition "make up a single sacred deposit of the Word of God, which is entrusted to the Church", and the magisterium is not independent of this, since "all that it proposes for belief as being divinely revealed is derived from this single deposit of faith."
The East–West Schism is the ongoing break of communion between the Roman Catholic and Eastern Orthodox churches since 1054. It is estimated that, immediately after the schism occurred, a slim majority of Christians worldwide were Eastern Christians comprised; most of the rest were Western Christians. The schism was the culmination of theological and political differences between Eastern and Western Christianity that had developed during the preceding centuries.
Papal primacy, also known as the primacy of the bishop of Rome, is a Roman Catholic ecclesiological doctrine concerning the respect and authority that is due to the pope from other bishops and their episcopal sees. The doctrine is accepted at a fundamental level by both the Catholic Church and Eastern Orthodox Church, though the two disagree on the nature of primacy.
The infallibility of the Church is the belief that the Holy Spirit preserves the Christian Church from errors that would contradict its essential doctrines. It is related to, but not the same as, indefectibility, that is, "she remains and will remain the Institution of Salvation, founded by Christ, until the end of the world." The doctrine of infallibility is premised on the authority Jesus granted to the apostles to "bind and loose" and in particular the promises to Peter in regard to papal infallibility.
The history of the Catholic Church is integral to the history of Christianity as a whole. It is also, according to church historian, Mark A. Noll, the "world's oldest continuously functioning international institution." This article covers a period of just under two thousand years.
The history of the papacy, the office held by the pope as head of the Catholic Church, spans from the time of Peter, to the present day. Moreover, many of the bishops of Rome in the first three centuries of the Christian era are obscure figures. Most of Peter's successors in the first three centuries following his life suffered martyrdom along with members of their flock in periods of persecution.
Papal supremacy is the doctrine of the Catholic Church that the Pope, by reason of his office as Vicar of Christ, the visible source and foundation of the unity both of the bishops and of the whole company of the faithful, and as pastor of the entire Catholic Church, has full, supreme, and universal power over the whole church, a power which he can always exercise unhindered: that, in brief, "the Pope enjoys, by divine institution, supreme, full, immediate, and universal power in the care of souls."
The doctrines of Petrine primacy and papal primacy are perhaps the most contentiously disputed in the history of Christianity. Theologians regard the doctrine of papal primacy as having gradually developed in the West due to the convergence of a number of factors, e.g., the dignity of Rome as the only apostolic see in the West; the tradition that both Peter and Paul had been martyred there; Rome's long history as a capital of the Roman Empire; and its continuing position as the chief center of commerce and communication.
Papal infallibility is a dogma of the Catholic Church which states that, in virtue of the promise of Jesus to Peter, the Pope when he speaks ex cathedra is preserved from the possibility of error on doctrine "initially given to the apostolic Church and handed down in Scripture and tradition". It does not mean that the pope cannot sin or otherwise err in most situations.
Pope Benedict XVI, who led the Roman Catholic Church as Pope from 2005 to 2013, continued manouevring the Church through the dynamics of modernity, which the Church had begun engaging in with the Second Vatican Council. Because the question of religious pluralism is a key issue raised by modernity, ecumenism, the establishment of harmony and dialogue between the different Christian denominations, is a significant concern of a post Second Vatican Council Church. Pope Benedict XVI's approach has been characterised as leaning toward the conservative while still being expansive and engaged, involving the full breadth of Christendom, including the Orthodox Churches and Protestant churches, as well as freshly engaging with other Christian bodies considered by Roman Catholics to be more heterodox, such as the Church of Jesus Christ of Latter-day Saints.
The following outline is provided as an overview of and topical guide to the Catholic Ecumenical Councils.
Heresy in the Catholic Church denotes the formal denial or obstinate doubt of a core doctrine of the Catholic Church. Heresy has a very specific meaning in the Catholic Church and there are four elements which constitute formal heresy; the person in question must have had a valid Christian baptism; the person claims to still be a Christian; the person publicly and obstinately denies or positively doubts a truth that the Catholic Church regards as revealed by God; and lastly, the disbelief must be morally culpable, that is, there must be a refusal to accept what is known to be a doctrinal imperative. Therefore, to become a heretic, and thus automatically lose communion with the Church and therefore no longer truly be Catholic, one must deny or question a truth that is taught as the word of God, and at the same time know that the Church teaches it as "de fide". If the person denied or questioned a doctrine that is "de fide", but only out of ignorance and in good faith, that person is not considered a heretic by the Catholic Church, though it is an expression of "material heresy".