The development of modern medicine began in the 16th century when Dr. Andreas Vesalius overthrew the previously uncontested medical dogma of the Greek physician Galen. Medical progress had been hindered for more than a millennium by strict adherence to Galen's authority. Flemish-born Vesalius challenged the political and societal forces of the time. At the University of Padua, he studied and later taught human anatomy by performing dissections. His discoveries were published in 1543 in his monumental De Humani Corporis Fabrica. Controversy led to his resignation from the University of Padua. His magnum opus was interpreted as a challenge to both academia and the church. He went to Spain, where he served as personal physician to Emperor Charles V. After almost 20 years in Spain, he became involved in an unfortunate incident that incurred the condemnation of the Inquisition. The royal court's intervention saved Vesalius from being burned at the stake, however, and he was ordered to make a pilgrimage to Jerusalem to atone for his error. On the return voyage, he became ill and died on the Greek island of Zante.