April 20, 1139: The Second Lateran Council, led by Pope Innocent II and attended by 1,000 church leaders, opens in Rome. The council focused on reforming the church in the wake of the East-West schism (1054) and preserving the temporal possessions of the clergy.
April 20, 1233 (some say 1232): Pope Gregory IX appoints full-time papal inquisitors and gives the Dominican order authority to carry out the Inquisition. For their vigilant and persistant work, the order won the moniker "Domini canes" or "God's dogs.
April 20, 1441: At the Council of Florence, Pope Eugenius IV issues the bull "Etsi non dubitemus," declaring the pope to be superior to church councils.
April 20, 1494: Johann Agricola, Saxon theologian and reformer, is born. He studied under Martin Luther at Wittenberg, and the two worked closely until Agricola embraced antinomianism—an overextension of the doctrine of "justification by faith" that asserted Christians are exempt from the need to observe any moral law. A violent controversy with Luther began, and it persisted even after Agricola recanted (Luther was one of very few who refused to accept the recantation).
April 20, 1718: David Brainerd, missionary to New England's Native Americans, is born in Haddam, Connecticut. Expelled from Yale for attending a revival meeting, Brainerd attained fame after his death (at age 29, from tuberculosis) when Jonathan Edwards published his journal. The diary inspired countless other missionaries, including William Carey, who is called "the father of modern missions" (see issue 8: Jonathan Edwards and issue 77: Jonathan Edwards).
April 20, 1853: Fugitive slave Harriet Tubman, who had escaped from the eastern shore of Maryland four years earlier, makes a return trip to the South to rescue other slaves. By the time slavery was abolished, she had made 19 such trips, liberating at least 300 fellow African Americans (see issue 62: Bound for Canaan).
May 31, 1578: Italian archaeologist Antonio Bosio discovers the Christian catacombs in Rome. Some have mistaken them for places of refuge or worship, but Christians used them mainly as burial chambers.
May 31, 1638: Puritan pastor Thomas Hooker arrives in what is now Connecticut, after leaving Massachusetts because of a rivalry with Roger Williams. The minister also helped organize America's first federal government, the United Colonies of New England (see issue 41: The American Puritans).