Luther started teaching at the university in Wittenberg in 1508, as an Augustinian monk, settling permanently in the town in 1511 when he was appointed to the Chair of Biblical Studies. In 1517 he began a protest against certain Church practices: mainly against the sale of Indulgences, a scheme that allowed people to "offset" some or all of their sins by paying money to the Church [Rather like 'carbon offsetting' today? Ed]. Many of the great mediaeval cathedrals in Europe had been financed in this way – as indeed was Luther's own university in Wittenberg – and the then Pope Leo X was counting on the ploy to pay for rebuilding St Peter's in Rome.
Objections to the sale of indulgences had bubbled under the surface for some time, led by thinkers such as the Czech philosopher Jan Hus (1372-1415), whom I'd met (so to speak) in Prague; but Martin Luther brought matters to a head by writing his 95 Theses, setting out his views, and allegedly nailing them to the door of Wittenberg's Schlosskirche. They were probably also printed, using the latest technology of the time. In fact his action was not as dramatic as it sounds as it was the accepted practice at the time as the way to start a scholarly debate, but the Church was not impressed, and in 1520 the Pope issued a decree (a Papal bull) threatening him with excommunication unless he retracted his views.
Luther publicly burned the Papal bull, along with a book of Church law and other books; an oak tree – now known as the Luther Oak [Luther-Eiche] – was later planted at the site of the burning, at the end of Collegienstrasse, to commemorate the event (the present tree is far too young to be the original). Luther was summoned to appear before the Reichstag zu Worms, the general assembly of the Holy Roman Emperor in the town of Worms, on the Rhine [in English, the Diet of Worms, pronounced 'dee-et of vorms'], in 1521, where he was excommunicated and declared a heretic (effectively condemned to death) on 25 May 1521.
Prince Frederick III, the Elector of Saxony, had obtained an agreement that if Luther appeared at Worms he would be promised safe passage to and from the meeting. In fact Frederick arranged for Luther to be captured during the return journey, for his own safety, and bundled off to the Wartburg at Eisenach, where he hid for 10 months under an assumed name. He returned to Wittenberg on 6 March 1522 to help quell local unrest by radicals, and to continue his battle against what he considered unacceptable practices in the Church. In 1525, at the age of 42, he married 26-year-old Katharina von Bora, and they moved into part of the former monastery in the town.
Luther was supported by his friend the brilliant academic Philipp Melanchthon (1497-1560), who had come to Wittenberg as Professor of Greek in 1518 at the age of 21, having studied at the University of Heidelberg since he was just 13. Melanchthon was born Philipp Schwarzerd (literally 'black earth'), but changed his name on the advice of his great-uncle Johann Reuchlin, the Humanist and scholar of Greek and Hebrew, into the Greek equivalent 'Melanchthon' [Μελαγχθων]. It was Melanchthon, with his sharper intellect, who was later responsible for the precise definition of the Lutheran faith in the Augsburg Confession.
There are statues of both Luther and Melanchthon in the main square: Luther's is by Johann Gottfried Schadow, and was erected in 1821 under a canopy designed by the German architect Schinkel; Melanchthon's statue was added in 1860, in a similar style.