Holy See. 1184: Pope Lucius III bans the Waldensians. October 2, 1187: The Siege of Jerusalem. Ayyubid forces led by Saladin capture Jerusalem, prompting the Third Crusade. 1188: Pope Innocent III issued a bull that proclaimed the emancipation of all slaves. January 8, 1198: Lotario de' Conti di Segni elected Pope Innocent III. His pontificate is often considered the height of the temporal power of the papacy. April 13, 1204: Sack of Constantinople by the Fourth Crusade. Beginning of Latin Empire of Constantinople. 1205: Saint Francis of Assisi becomes a hermit, founding the Franciscan order of friars. November 11, 1215: Fourth Ecumenical Lateran Council opened by Pope Innocent III. November 30, 1215: Fourth Ecumenical Lateran Council is closed by Pope Innocent III. Seventy decrees were approved, the pre-Thomistic definition of transubstantiation being among them. 1215: Cardinal Stephen Langton, one of the early Catholic English cardinals, became an important player in the dispute between King John and Pope Innocent III. The tense situation led to the signing and promulgation of the Magna Charta. 1216: The Order of Preachers (Dominican Order) founded by Saint Dominic is approved as a body of Canons Regular by Pope Honorius III on December 22 (Pope Innocent III having died in July). 1229: Inquisition founded in response to the Cathar heresy, at the Council of Toulouse. 1231: Charter of the University of Paris granted by Pope Gregory IX. 1233: In a papal bull or charter, Pope Gregory IX gave graduates of Cambridge University the right to teach "everywhere in Christendom". Other popes encouraged researchers and scholars from other universities to visit Cambridge, study there, and give lecture courses. 1241: The death of Ögedei Khan, the Great Khan of the Mongols, prevented the Mongols from further advancing into Europe after their easy victories over the combined Christian armies in the Battle of Liegnitz (in present-day Poland) and Battle of Mohi (in present-day Hungary). 1245: First Council of Lyon. Excommunicated and deposed Emperor Frederick II. 1248: Commencement year of the building of Cologne Cathedral; later finished in 1880. 1254: Pope Innocent IV grants to Oxford University a charter (via the papal bull, Querentes in argo). 1274: Second Council of Lyon; Catholic and Orthodox Churches temporarily reunited. Thomas Aquinas dies. 1295: Marco Polo arrives home in Venice. February 22, 1300: Pope Boniface VIII published the Bull Antiquorum fida relatio; first recorded Holy Year of the Jubilee celebrated. 1298: St. Gregory