Marranos were originally Jews living in the Iberian Peninsula who converted or were forced to convert to Christianity, some of whom may have continued to practice Judaism in secret. The term came into later use in 1492 with the Castilian Alhambra Decree, reversing protections originally in theTreaty of Granada (1491).

The converts were also known as cristianos nuevos (Spanish) or cristãos-novos (Portuguese), which mean New Christians; conversos (the converted); or anusim(Hebrew for “forced”).

Some Portuguese conversos or cristãos-novos continued to practice as crypto-Jews. In the early 20th century, historian Samuel Schwartz wrote about crypto-Jewish communities discovered in northeastern Portugal (namely, Belmonte, Bragança, Miranda, and Chaves). He claimed that members had managed to survive more than four centuries without being fully assimilated into the Old Christian population. The last remaining crypto-Jewish community in Belmonte officially returned to Judaism in the 1970s and opened a synagogue in 1996. In 2003, the American Sephardi Federation founded the Belmonte Project to raise funds to acquire Judaic educational material and services for the Belmonte community, who then numbered 160-180.

Two documentary films are known to have been made in north-eastern Portugal where present day descendants of Marranos were interviewed about their lives. In 1974 for The Marranos of Portugal, the Israel Broadcasting Authority (IBA) sent reporter Ron Ben-Yishai to carry out interviews with families about their religious practice. After being asked to prove he knew Hebrew before they would talk, he found people still reluctant to talk openly but did eventually gain a remarkable insight into their version of Jewish customs, prayers and songs. The film was commended at the 1976 Jerusalem Jewish Film and TV Festival. Another documentary, The Last Marranos, was made by the New York Jewish Media Fund in 1997.

After the expulsion of Jews and Muslims from Spain (1492) and Portugal (1497), conversos continued to be suspect in times of social strain. In Lisbon in 1506, a months-long plague caused people to look for scapegoats. Some became suspicious that conversos might be practicing Judaism and therefore be at fault. On April 17, 1506, several conversos were discovered who had in their possession “some lambs and poultry prepared according to Jewish custom; also unleavened bread and bitter herbs according to the regulations for the Passover, which festival they celebrated far into the night.” Officials seized several, but released them after a few days.

On the same day on which the conversos were freed, the Dominicans displayed a crucifix and a reliquary in glass from which a peculiar light issued in a side-chapel of their church, where several New Christians were present. A New Christian who tried to explain the miracle as due to natural causes was dragged from the church and killed by an infuriated woman. A Dominican roused the populace still more. Friar João Mocho and the Aragonese friar Bernardo, crucifix in hand, were said to go through the streets of the city, crying “Heresy!” and calling upon the people to destroy the conversos. Attracted by the outcry, sailors fromHolland, Zeeland and others from ships in the port of Lisbon, joined the Dominicans and formed a mob with local men to pursue the conversos.

The mob dragged converso victims from their houses and killed some. Old Christians who were in any way associated with New Christians were also attacked. The mob attacked the tax-farmer João Rodrigo Mascarenhas, a New Christian; although a wealthy and distinguished man, his work also made him resented by many. They demolished his house. Within 48 hours, many “conversos” were killed; by the third day all who could have escaped, often with the help of other Portuguese. The killing spree lasted from 19 to 21 April, in what came to be known as the Lisbon Massacre.

King Manuel severely punished those who took part in the killings. The ringleaders and the Dominicans who encouraged the riot were also executed. Local people convicted of murder or pillage suffered corporal punishment and their property was confiscated. The king granted religious freedom for 20 years to all conversos in an attempt at compensation. Lisbon lost Foral privileges. The foreigners who had taken part generally escaped punishment, leaving with their ships.

New Christians were attacked in Gouvea, Alentejo, Olivença, Santarém, and other places. In the Azores and the island of Madeira, mobs massacred former Jews. Because of these excesses, the king began to believe that a Portuguese Inquisition might help control such outbreaks.

The Portuguese conversos worked to forestall such actions, and spent immense sums to win over the Curia and most influential cardinals. Spanish and Portuguese conversos made financial sacrifices. Alfonso Gutierrez, Garcia Alvarez “el Rico” (the rich), and the Zapatas, conversos from Toledo, offered 80,000 gold crowns to Emperor Charles V if he would mitigate the harshness of the Inquisition (Revue des Etudes Juives, xxxvii, p. 270 et seq.).

The Mendes of Lisbon and Flanders also tried to help. None were successful in preventing Portugal from introducing the Holy Office in 1478. The conversos suffered immensely both from mob violence and interrogation and testing by the Inquisition. Attacks and murders were recorded at Trancoso, Lamego, Miranda, Viseu, Guarda, and Braga.

At Covilhã, there were rumors that the people planned to massacre all the New Christians on one day. In 1562, prelates petitioned the Cortes to require conversos to wear special badges, and to order Jewish descendants to live in ghettos (judiarias) in cities and villages as their ancestors had before the conversions.