The infamous Spanish Inquisition was an official government institution which carried out an organized campaign to wipe out heresy, primarily by Jews who claimed to have converted to Christianity but who still practiced Judaism in secret. It was strongest in Catholic Aragon and Castile, ruled by Ferdinand and Isabella, respectively, in what is now Spain. At its height, it reached as far as Venice and Scandinavia. The institution existed from 1481 until 1820, and was characterized by extreme cruelty and torture. Many thousands were burnt alive at the stake.
Much of the Iberian peninsula had been ruled by the Moors, and the southern regions, particularly Granada, were heavily populated by Muslims. Granada was still under Moorish rule -- they were not to be expelled until 1492. The large cities, especially Seville, Valladolid, capital of Castile, and Barcelona, capital of Aragon, had large Jewish populations centered in Juderias. Many Jews had left Barcelona after the 1391 massacres, but there was still a sizeable Jewish population.
There was a long tradition of Jewish service to the Crown of Aragon. Ferdinand's father, John of Aragon, appointed Abiathar Crescas, a Jew, as his court astrologer. Jews held many prominent posts, both religious and political. Pedro de la Caballeria, a Marrano, played a major role in arranging Ferdinand's marriage. Castile even had an unofficial Crown Rabbi, a professing Jew.
While Isabella was a devout Catholic, Ferdinand was not above using religion as a means of controlling his people. He wanted the Jewish and Muslim religions wiped out in his domains, and the Inquisition was his method for achieving that. Many historians believe the Spanish Inquisition was instituted as a way of weakening Ferdinand's primary political opposition at home. It is also possible that there was a financial motivation. Jewish financiers had provided many of the funds which Ferdinand's father used to pursue the alliance by marriage with Castile, and many of these debts were wiped out by the condemnation of the noteholder.
Technically, the Spanish Inquisition was not an ecclesiastical operation but was organized and conducted by the government. Ferdinand was an astute politician, and developed close ties with St. Peter's as part of his political maneuvering, aimed at consolidating the independent realms (joined by his marriage to Isabella) into a single state to be left to his heir. However, he did not want the Pope to control the Inquisition in Spain, as he was jealous of any other power within his borders.
The Pope did not want the Inquisition established in Spain at all, but Ferdinand insisted. He prevailed upon Rodrigo Borgia, then Bishop of Valencia and a cardinal, to lobby Rome on his behalf. Borgia was partially successful, as Pope Sixtus IV sanctioned the Inquisition only in the state of Castile. Later, Borgia was to have Spain's support for his own papacy as Pope Alexander VI.
Ferdinand and Isabella appointed Tomas de Torquemada in 1481 to investigate and punish conversos -- Jews and Moors (Muslims) who claimed to have "converted" to Catholicism but continued to practice their "former" religion in secret. Some disguised Jews had even been ordained as priests and even bishops. Detractors also called converted Jews Marranos, a pejorative word that can also be translated "pigs".
Of the several Inquisitions, the Spanish Inquisition had by far the worst record for corruption and malice. The Inquisition began in the city of Seville, and the cruelty and terror for which it is known began there immediately. The "guilty" often had their hands chopped off before they were burnt, often alive.
Thousands of Jews fled the city. By law, their property was confiscated by the Crown.
Spain was not a single country but a confederation of states, each with their own administrations. Ferdinand had not yet consolidated his power across the Iberian peninsula. The local administrations in the provinces of Aragon did their best to prevent the spread of the Inquisition to their territories. They still remembered the horrors of 1391, when persecution of the Jews resulted in widespread privation and economic disaster. The parliament of Catalonia, called the Cortes, refused the Inquisition admittance to Barcelona. The people also were strongly opposed, and the Inquisitor who Ferdinand installed in Saragossa Cathedral was assassinated by New Christians.
The Pope disapproved of the extreme measures being taken by Ferdinand, and categorically disallowed their spread to the kingdom of Aragon. He alleged that the Inquisition was a cynical ploy by Ferdinand and Isabella to confiscate the Jews' property. Despite his title of "Most Catholic King", and his ongoing attempts to woo the Pope to his side politically, Ferdinand continued to resist direct Papal influence in his lands. He decided to use strongarm tactics against the Pope.
Ferdinand had some important levers he could use to bend the Pope to his will. Venice, traditionally the defender against the Turks in the East, was greatly weakened after a protracted war with them which ran from 1463 to 1479. The Turks had taken possession of Greece and the Greek islands. France, as always, was looking for signs of weakness which it could use to its advantage. And in the midst of all these threats, in August of 1480 the Sultan had attacked Italy itself, at the port of Otranto, with several thousand janissaries. They pillaged the countryside for three days, largely unopposed.
Under these conditions, Ferdinand's position in Sicily -- he was king of Sicily as well as Aragon and several other kingdoms -- gave him the leverage he needed. He threatened to withhold military support of the Holy See, and the Pope relented.
Sixtus then blessed the royal institution of the Spanish Inquisition. Ferdinand had won everything he sought: the Inquisition was under his sole control, but had the blessing of the Pope, and the royal coffers were swelling with the loot of the Jewish victims.
Sixtus IV died in 1484, and was succeeded by Pope Innocent VIII. Unlike his predecessor, Innocent supported the Spanish Inquisition wholeheartedly, going out of his way to facilitate it. He ordered all Catholic monarchs to extradite fleeing Jews back to Spain where they could stand trial.
But "trial" is really not the word for the tribunals of the Spanish Inquisition. There were none of the legal rights honored in most modern societies. A person could be condemned and executed if a single person made an allegation against them. Many persons made such accusations out of revenge, or to gain rewards from the Crown. Very probably the Crown itself was behind some of the allegations, in the desire to appropriate wealthy Jews' lands, property and valuables.
Hard numbers are hard to put down, but estimates are that between four and eight thousand Jews were burnt alive during the fifteen years Torquemada held the office of Grand Inquisitor, as well as a smaller number of Moriscos, or Moorish converts. Many more died or spent many years in the prisons and dungeons. It is estimated that around 32,000 people were burnt alive during the entire 340 years of the Inquisition's existence.
The Inquisition succeeded in spreading as far as Venice, Germany and Scandinavia, although it was never as powerful or as abusive in those remote regions as it was in Spain. It had little impact in the German and Scandinavian countries. The Inquisition was never instituted in England, but Christopher Columbus carried it with him to the New World.
The Inquisition was used against Protestants in the Netherlands during their war for independence from Spain.