The Fourth Council of the Lateran or Lateran IV was convoked by Pope Innocent III in April 1213 and opened at the Lateran Palace in Rome on 11 November 1215. Due to the great length of time between the council's convocation and its meeting, many bishops had the opportunity to attend this council, which is considered by the Catholic Church to be the twelfth ecumenical council. The council addressed a number of issues, including the sacraments, the role of the laity, the treatment of Jews and heretics, and the organization of the church. In the case of Jews and Muslims, this included compelling them to wear distinctive badges to prevent social contact "through error".

The Council is viewed as both opening up many reforms, and as formalising and enforcing intolerance in European society, both to heretics and Jews, and thus playing a role in the development of systemic European antisemitism.

Innocent III first mooted organizing an ecumenical council in November 1199.^[1] In his letter titled Vineam Domini, dated 19 April 1213,^[2] the Pope writes of the urgent need to recover the Holy Land and reform the Church.^[3] The letter, which also served as a summons to an ecumenical council, was included alongside the Pope's papal bull Quia maior.^[1] In preparing for the council, the Pope spearheaded the extensive refurbishment of the old St. Peter's Basilica, which he designated as the "centrepiece for display and decoration" during the council. The lunette of the main door leading to the tomb of St. Peter had engravings of Old Testament prophets and twenty-four bishops, alongside the messages, "Feed your Sheep" and "This is the Door of the Sheep".^[4]

The measures against the Jews were the culmination of hostility during Innocent's reign as Pope, itself informed by a background of greater hostility to the Jews generated in part by the Crusades. Innocent for example waged a novel campaign against the Talmud as part of the campaign against heresy, claiming that the Talmud was an invention of the Rabbis, and the Jews should be restricted to using Biblical texts for their faith. This was the first time that the Catholic church had tried to directly regulate the practice of Judaism.^[5]

Innocent III deliberately chose for the Fourth Council to meet in November, during which there were numerous feast days.^[6] A preliminary legal session took place on 4 November,^[7] while the opening ceremony of the council was held on St. Martin's Day and began with a private morning Mass.^[6] Afterwards, at the start of the first plenary session in the Lateran Palace, the Pope led the singing of "Veni Creator Spiritus"^[8] and preached about Jesus' words to his disciples at the Last Supper,^[9] quoting from Luke 22.^[10] In his next two sermons, one on the need to recover the Holy Land and the other on dealing with heretics,^[11] the Pope was joined on stage by Raoul of Mérencourt and Thedisius of Agde respectively.^[7]

On 14 November, there were violent scenes between the partisans of Simon de Montfort among the French bishops and those of the Count of Toulouse. Raymond VI of Toulouse, his son (afterwards Raymond VII), and Raymond-Roger of Foix attended the council to dispute the threatened confiscation of their territories; Bishop Foulques and Guy de Montfort (brother of Simon de Montfort) argued in favour of the confiscation. All of Raymond VI's lands were confiscated, save Provence, which was kept in trust to be restored to Raymond VII.^[12] Pierre-Bermond of Sauve's claim to Toulouse was rejected and Toulouse was awarded to de Montfort, while the lordship of Melgueil was separated from Toulouse and entrusted to the bishops of Maguelonne.^[12]

The next day, in a ceremony attended by many council participants, the Pope consecrated the Basilica of Santa Maria in Trastevere,^[6] which had been rebuilt by Callixtus II.^[13] Four days later, the anniversary celebration at St. Peter's Basilica brought together such a large gathering that the Pope himself had trouble entering the premises.^[13]

The second plenary session was held on 20 November; the Pope was scheduled to preach about church reform, but proceedings were disrupted by bishops who opposed the designation of Frederick II as Holy Roman Emperor.^[14] The council concluded on 30 November, Saint Andrew's Day, during which the Pope preached on the Nicene Creed and concluded his remarks by raising up a relic of the True Cross.^[14] The archbishop of Mainz attempted to interrupt the speech, although he complied with the Pope's raising of his hand—a command to stay silent.^[15]

Lateran IV had three objectives: crusading, Church reform, and combating heresy.^[16] The seventy-one Lateran canons, which were not debated, were only formally adopted on the last day of the council;^[17] according to Anne J. Duggan, the "scholarly consensus" is that they were drafted by Innocent III himself.^[18] They cover a range of themes including Church reform and elections, taxation, matrimony, tithing, simony, and Judaism.^[19] After being recorded in the papal registers, the canons were quickly circulated in law schools.^[20] Effective application of the decrees varied according to local conditions and customs.^[21]

While the proceedings were not officially recorded, unlike in previous councils, evidence of the events have been found in various manuscripts by observers of the council.^[25] The Chronica Majora by Matthew Paris contains a line drawing of one of the sessions at the council which his abbot William of St Albans had personally attended.^[26] An extensive eyewitness account by an anonymous German cleric was copied into a manuscript that was published in 1964, in commemoration of the Second Vatican Council, and is now housed at the University of Giessen.^[27]

Henry of Segusio likened the council to the "four great councils of antiquity".^[28] Lateran IV is sometimes referred to as the "Great Council of the Lateran" due to the presence of 404 or 412 bishops (including 71 cardinals and archbishops) and over 800 abbots and priors representing some eighty ecclesiastical provinces,^[18][29] together with 23 Latin-speaking prelates from the Eastern Orthodox Church^[28] and representatives of several monarchs, including Frederick II, Otto IV, the Latin Emperor of Constantinople, John, King of England, Andrew II of Hungary, Philip II of France, and the kings of Aragon, Cyprus, and Jerusalem.^[28] This made it the largest ecumenical council between the Council of Chalcedon and the Second Vatican Council;^[30] Anne J. Duggan writes that "it was the largest, most representative, and most influential council assembled under papal leadership before the end of the fourteenth century."^[31] According to F. Donald Logan, "the Fourth Lateran Council was the most important general council of the church in the Middle Ages",^[32] whose effects "were felt for centuries."^[33]