May 11

Roman Emperor Constantine the Great dedicates the rebuilt city of Byzantium as "New Rome," establishing it as capital of the Eastern Roman Empire.

Roman Emperor Constantine the Great formally dedicated the rebuilt and expanded city of Byzantium as his new imperial capital, renaming it New Rome in an elaborate ceremony, though it would soon become popularly known as Constantinople in his honor. The city served as the seat of what developed into the Byzantine Empire for over a thousand years.

Roman emperor Constantine the Great dedicates the city of Constantinople as his new capital.

Constantine chose the ancient Greek city of Byzantium, on the strategic Bosphorus strait, as the site for a new eastern capital befitting his empire. Renamed Constantinople in his honor, the city grew into one of history's great metropolises and would remain the capital of the Byzantine Empire for over a thousand years, until its fall in 1453.

A printed copy of the Diamond Sutra is produced in China, regarded as the earliest dated printed book known to survive.

A copy of the Buddhist scripture known as the Diamond Sutra was printed in Dunhuang, China, using carved woodblock printing techniques, and it survives today, now held in the British Library, as the earliest dated printed book known to exist, predating Johannes Gutenberg's famous Bible by nearly six centuries.

Edgar the Peaceful is crowned King of England at Bath Abbey in the first English coronation ceremony.

Edgar had reigned since 959, but at Bath Abbey he underwent an elaborate coronation designed largely by Archbishop Dunstan of Canterbury. The ceremony, held on Whit Sunday, established rites and symbolism—anointing, crowning, oath-taking—that shaped every English coronation afterward, including those still used today. Historians consider it the moment the English monarchy's ceremonial tradition truly began.

Matilda of Flanders is crowned Queen of England at Westminster Abbey.

Matilda, wife of William the Conqueror, had remained in Normandy managing affairs while William secured his new kingdom after 1066. Her coronation, presided over by Archbishop Ealdred of York, made her the first queen crowned in England following the Norman Conquest, formally cementing the new Anglo-Norman royal line and her own considerable political influence in the kingdom.

Louis IX of France and James I of Aragon sign the Treaty of Corbeil, settling longstanding feudal territorial disputes.

King Louis IX of France and King James I of Aragon signed the Treaty of Corbeil, resolving longstanding feudal territorial and overlordship disputes between their respective kingdoms in the border regions of southern France and Catalonia, with each monarch renouncing competing claims to the other's core territories.

Ottoman naval forces defeat a Spanish fleet at the Battle of Djerba, marking the height of Ottoman Mediterranean naval power.

The Ottoman navy under the command of the formidable corsair Turgut Reis decisively defeated a combined Spanish, Genoese, and Papal fleet at the Battle of Djerba off the coast of Tunisia, capturing thousands of prisoners and marking the high point of Ottoman naval dominance across the Mediterranean Sea.

British Prime Minister Spencer Perceval is assassinated in the House of Commons, the only British prime minister ever killed in office.

British Prime Minister Spencer Perceval was shot dead in the lobby of the House of Commons by John Bellingham, a merchant nursing a personal financial grievance against the government over unresolved compensation claims. Perceval remains, to this day, the only British prime minister ever assassinated while in office.

British Prime Minister Spencer Perceval is shot dead in the House of Commons.

Perceval was assassinated by John Bellingham, a merchant with a grievance over unpaid compensation from the government, who shot him in the lobby of the Commons. Perceval remains the only British prime minister ever assassinated. Bellingham was tried, convicted, and hanged within a week, while the killing briefly plunged Westminster into panic about political violence.

Indian rebel soldiers seize Delhi from British control during the Indian Rebellion of 1857.

Rebelling Indian sepoy soldiers seized control of Delhi from British colonial authorities after marching from Meerut, a major early flashpoint that rapidly expanded into the widespread Indian Rebellion of 1857 against East India Company rule, an uprising that ultimately led Britain to dissolve the company and assume direct crown control over India.

Rebel sepoys seize Delhi from British forces, escalating the Indian Rebellion.

Sepoys who had mutinied at Meerut marched on Delhi and proclaimed the aged Mughal emperor Bahadur Shah II as their leader, seizing the city from its small British garrison. The fall of Delhi transformed a mutiny into a wider rebellion against East India Company rule across northern India, one the British would spend over a year suppressing.

Minnesota is admitted to the Union as the 32nd U.S. state.

Minnesota was admitted to the Union as the 32nd U.S. state, having developed rapidly through fur trading, timber harvesting, and agricultural settlement in the decades following its organization as a formal U.S. territory, drawing waves of Scandinavian and German immigrants to its fertile farmland.

Fifty-six spectators die when fire sweeps through a stand at Bradford City's football ground.

A discarded cigarette is believed to have ignited rubbish beneath the wooden stand at Valley Parade during a match against Lincoln City. The fire spread with terrifying speed through the aging timber structure, killing 56 people and injuring hundreds more. The disaster led to sweeping new safety regulations for British football grounds, including bans on wooden stands.

IBM's Deep Blue defeats world chess champion Garry Kasparov, becoming the first computer to beat a reigning champion in a classic match format.

IBM's chess-playing supercomputer Deep Blue defeated reigning world champion Garry Kasparov in the deciding game of a six-game rematch, becoming the first computer system to beat a sitting world champion under standard tournament time controls, a landmark moment widely seen as a turning point in public perception of artificial intelligence.

Chess computer Deep Blue defeats world champion Garry Kasparov in their rematch.

IBM's Deep Blue won the deciding sixth game of the six-game match, making it the first computer to defeat a reigning world chess champion in a full match under standard time controls. Kasparov, who had won an earlier match against an older version of the machine, alleged foul play, but the result is widely remembered as a landmark moment for artificial intelligence.

India conducts three underground nuclear tests at Pokhran, becoming a declared nuclear power.

The tests, code-named Operation Shakti, included a fusion device and were followed two days later by two more explosions. They confirmed India's nuclear weapons capability, ending decades of ambiguity, and provoked international sanctions along with a rapid nuclear test response from neighboring Pakistan later that month.

Space Shuttle Atlantis launches on its final servicing mission to the Hubble Space Telescope.

Space Shuttle Atlantis launched on the fifth and final Hubble Space Telescope servicing mission, during which astronauts conducted a grueling series of challenging, high-risk spacewalks to repair failing components and install new scientific instruments, significantly extending the aging telescope's operational life well beyond its original planned lifespan.

Space Shuttle Atlantis launches on the final Hubble Space Telescope servicing mission.

STS-125 sent seven astronauts to repair and upgrade the aging telescope, installing new instruments, batteries, and gyroscopes during five spacewalks. It was the last of five servicing missions to Hubble and one of the riskiest shuttle flights ever flown, since Atlantis could not reach the International Space Station if damaged, requiring a rescue shuttle on standby.

David Cameron becomes British prime minister, forming the country's first coalition government since World War II.

David Cameron became British prime minister after leading the Conservative Party into a formal coalition government with the smaller Liberal Democrats party, following an inconclusive general election result. It was the first coalition government to govern the United Kingdom since the wartime national unity government of the Second World War.

David Cameron becomes Prime Minister of the United Kingdom, forming a coalition government.

After an inconclusive general election left no party with a majority, Cameron's Conservatives struck a coalition deal with Nick Clegg's Liberal Democrats. It was Britain's first coalition government since the Second World War, with Cameron becoming the youngest prime minister since 1812 and Clegg taking the post of deputy prime minister.