April 21

According to Roman tradition, the city of Rome is founded by Romulus.

According to Roman legend recorded by later historians, the twin brothers Romulus and Remus founded the city of Rome on the Palatine Hill, with Romulus becoming the city's first king after killing his brother in a dispute over the new settlement's boundaries. While the precise historical founding date remains uncertain, ancient Romans commemorated this legendary date annually.

Roman consul Aulus Hirtius defeats Mark Antony's forces at the Battle of Mutina.

Roman consul Aulus Hirtius, fighting alongside Octavian's forces, defeated troops loyal to Mark Antony at the Battle of Mutina in northern Italy, though Hirtius was killed in the fighting alongside his fellow consul Pansa days earlier. The victory temporarily weakened Antony's position but ultimately failed to prevent his later alliance with Octavian in the Second Triumvirate.

Henry VIII ascends to the English throne following the death of his father, Henry VII.

The 17-year-old Henry VIII ascended to the English throne following the death of his father, Henry VII, inheriting a relatively stable and well-funded kingdom. His subsequent 38-year reign would dramatically reshape English religion, government, and society, most notably through his break with the Catholic Church and establishment of the Church of England.

King Rama I establishes Bangkok as the new capital of Siam, founding the Chakri dynasty that rules Thailand today.

King Rama I founded Bangkok as the new capital of Siam and established the Chakri dynasty, which continues to rule Thailand today, making it one of the world's longest-reigning royal houses. The new capital was strategically located along the Chao Phraya River, offering better defensive and trade advantages than the previous capital.

Texan forces under Sam Houston defeat Mexican General Antonio López de Santa Anna at the Battle of San Jacinto, securing Texan independence.

Texan forces under Sam Houston launched a surprise attack on Mexican troops during their afternoon siesta at the Battle of San Jacinto, achieving a swift and decisive victory that led to the capture of Mexican General Antonio López de Santa Anna and secured Texan independence in a battle lasting only about eighteen minutes.

German fighter ace Manfred von Richthofen, known as the "Red Baron," is shot down and killed over France.

German fighter ace Manfred von Richthofen, known as the "Red Baron" and credited with 80 confirmed aerial victories, the most of any pilot in World War I, was shot down and killed while pursuing an Allied aircraft over the Somme battlefield in France, ending the career of the war's most celebrated flying ace.

Brazil's new capital city, Brasília, is officially inaugurated, replacing Rio de Janeiro.

Brazil's newly constructed capital city, Brasília, built from scratch in the country's interior according to a bold modernist master plan, was formally inaugurated, replacing Rio de Janeiro as the seat of government. The project aimed to spur development in Brazil's underpopulated interior and remains a celebrated example of large-scale urban planning.

The Century 21 Exposition, the first World's Fair held in the U.S. since World War II, opens in Seattle.

The Century 21 Exposition, the first World's Fair held in the United States since before World War II, opened in Seattle, Washington, showcasing space-age technology and futuristic design themes that reflected the era's optimism about scientific progress. The fair left behind the iconic Space Needle as a lasting landmark of the city.

Roughly 100,000 students gather in Beijing's Tiananmen Square to mourn reformist leader Hu Yaobang, an early spark of that year's pro-democracy protests.

Roughly 100,000 university students gathered in Beijing's Tiananmen Square to mourn the death of reformist Communist Party leader Hu Yaobang, whose removal from power years earlier had made him a symbol of political liberalization. The gathering marked an early spark of the broader pro-democracy demonstrations that would grow dramatically over the following weeks.

Coordinated Easter Sunday bombings at churches and hotels across Sri Lanka kill at least 269 people.

Coordinated suicide bombings struck churches during Easter Sunday services and luxury hotels across Sri Lanka, killing at least 269 people in the deadliest violence the country had experienced since the end of its civil war a decade earlier. The attacks, claimed by the Islamic State, exposed significant intelligence and security failures despite prior warnings.