The fifteenth day of August.
- 1248. The foundation stone of the Cologne Cathedral, built to house the relics of the Three Wise Men, was laid. Construction eventually completed in 1880.
- 1309. - The city of Rhodes, Greece surrenders to the forces of the catholic order of the Knights of St. John, completing their conquest of Rhodes. The knights establish their headquarters on the island, and rename themselves as the Knights of Rhodes. The order is currently known as the Sovereign Military Hospitaller Order of Saint John of Jerusalem, of Rhodes and of Malta.
- 1461. The Empire of Trebizond (a remnant of the Byzantine Empire) surrenders to the forces of Sultan Mehmet II. Emperor David is exiled and later murdered.
- 1534. Saint Ignatius of Loyola and six classmates took initial vows that would lead to the creation of the Society of Jesus in September of 1540.
- 1549. Jesuit priest Saint Francis Xavier comes ashore at Kagoshima and becomes the first modern missionary to Japan.
- 1843. The Cathedral of Our Lady of Peace in Honolulu, Hawaii is dedicated. Now the cathedral of the Roman Catholic Diocese of Honolulu, it is the oldest Roman Catholic cathedral in continuous use in the United States.
- 1195. Anthony of Padua, Portuguese saint (d. 1231)
- 1917. Oscar Romero, El Salvador Roman catholic priest (d. 1980)
- 1274. Robert de Sorbon, French theologian and founder of the Sorbonne (b. 1201)
- 1552. Hermann of Wied, German Catholic archbishop (b. 1477)
- 1666. Johann Adam Schall von Bell, German Jesuit missionary (b. 1591)
- RC Saints
- Saint Alfred (died 874)
- Saint Alipius, bishop
- Saint Arnulph, bishop of Soissons
- St. Arnoul/Saint Arnulphus
- St. MacCartan/Ard/Aed/Mac-Cartan (Ard), Bishop of Clogher, Ireland
- Saint Tarcisius
- Blessed Rupert (died 1145)
- Stanislaus Kostka
- Saint Napoleon (born on 15 August 1769), formerly celebrated in the First French Empire (1804-1814)
- Eastern Orthodoxy – Feast of the Dormition of the Theotokos, the commemoration of the death of Mary, the mother of Jesus.
- Feast day of the Assumption of Mary, the mother of Jesus, Holy Day of Obligation. Public Holiday in: Austria, Belgium, Cameroon, Chile, Côte d'Ivoire, Croatia, Cyprus, France, Greece, Italy, Lebanon, Lithuania, Luxembourg, Malta, Mauritius, Poland, Portugal, Slovenia and Spain.