At the root of the Walk to Canossa was a long-simmering row about the balance of power between pope and emperor, known as the Investiture Controversy. When relations broke down, Gregory formally excommunicated and deposed the emperor – the ultimate sanction in medieval Christendom. As his support began to erode, Henry felt compelled to take extraordinary measures.

After crossing the Alps in the first weeks of 1077, Henry dressed as a penitent, abandoning his shoes and putting on a monk’s hair shirt. It was in this attire that, on 25 January, he arrived at Canossa. When the pope refused him entry, Henry waited outside, praying on his knees in the snow. At last, on 28 January, the castle gate creaked open. Inside, Henry fell on his knees before the pope and asked for forgiveness, and then they took communion together.

Today, ‘going to Canossa’ has become a common expression denoting reluctant penance, especially in Germany. In reality, the effect was limited, as Henry and Gregory soon fell out again. But as a symbol of the conflict between Germany and the papacy, Canossa became enormously important. For many Lutherans, the emperor was the ‘first Protestant’. And when, in the 19th century, Otto von Bismarck launched his drive to curtail the powers of the Catholic church, he made his intentions very clear. “We will not,” he said, “go to Canossa.” | Written by Dominic Sandbrook

25 January 1308

Isabella, 12-year old daughter of Philip IV of France, weds King Edward II of England at Boulogne. The marriage will not be a success.

25 January 1533

Probable date of the secret marriage in the king’s private chapel at Whitehall of King Henry VIII and a pregnant Anne Boleyn.

25 January 1759

Birth in Alloway, Ayrshire of Robert Burnes, the eldest of the seven children of smallholder William Burnes and his wife Agnes. Later changing his surname to Burns, will grow up to become Scotland’s best-loved poet.

25 January 1882

English novelist, critic and queen of the Bloomsbury Group Virginia Woolf was born Adeline Virginia Stephen at Hyde Park Gate, Kensington. Her father, Leslie Stephen, was the founding editor of the Dictionary of National Biography.

25 January 1971

Idi Amin seized power in Uganda while the country’s president, Dr Milton Obote, was out of the country attending a Commonwealth conference in Singapore.