February 23

Byzantine Emperor Justinian I lays the foundation stone for the Hagia Sophia in Constantinople, which would become one of the greatest architectural achievements of the ancient world.

Justinian's Hagia Sophia, built to replace an earlier church destroyed during the Nika riots, was completed in under six years and its massive central dome was considered an engineering marvel of the ancient world. It served for centuries as the world's largest cathedral before later becoming a mosque and now a museum-mosque in modern Istanbul.

Mexican forces under Santa Anna begin the siege of the Alamo in San Antonio, Texas, a pivotal battle in the Texas Revolution.

The vastly outnumbered defenders of the Alamo mission, including figures like Davy Crockett and Jim Bowie, held out for thirteen days before being overwhelmed by Santa Anna's forces. Their defeat, though a military loss, became a galvanizing rallying cry, "Remember the Alamo," that helped Texas ultimately win its independence weeks later.

American forces under Zachary Taylor defeat a much larger Mexican army at the Battle of Buena Vista, boosting Taylor's political fortunes toward the presidency.

Taylor's outnumbered forces held their ground against a much larger Mexican army in rugged terrain, a defensive victory that, while not decisive to the war's outcome, boosted Taylor's national reputation and helped propel him to the U.S. presidency two years later.

Mass demonstrations erupt in Petrograd over bread shortages, marking the beginning of the February Revolution that would topple the Russian tsar.

Women textile workers and other demonstrators in Petrograd, protesting bread shortages and wartime hardship, were soon joined by soldiers who refused orders to suppress them, rapidly escalating into a revolution that forced Tsar Nicholas II to abdicate within days, ending three centuries of Romanov rule.

Chemist Glenn T. Seaborg and colleagues first produce and isolate plutonium, a discovery central to the later development of nuclear weapons.

Seaborg's team produced plutonium by bombarding uranium with particles in a cyclotron, a discovery kept secret during wartime due to its critical role in nuclear weapons development. Plutonium became the fissile material used in the first atomic bomb tested and the weapon dropped on Nagasaki.

U.S. Marines raise the American flag atop Mount Suribachi during the Battle of Iwo Jima, producing one of the most famous photographs of World War II.

The flag-raising atop Mount Suribachi, captured in Joe Rosenthal's Pulitzer Prize-winning photograph, became one of the most reproduced images in history and later the basis for the U.S. Marine Corps War Memorial, even though the actual battle for Iwo Jima continued for weeks afterward.

Combined Filipino and American forces liberate Manila from Japanese occupation after weeks of fierce urban fighting.

The liberation of Manila came after weeks of brutal urban combat in which retreating Japanese naval forces massacred tens of thousands of Filipino civilians, leaving much of the once-elegant "Pearl of the Orient" in ruins, among the most devastated Allied capital cities of the entire war.

Civil Guard officer Antonio Tejero leads an attempted coup, storming Spain's parliament and briefly holding lawmakers hostage before the plot collapsed.

Tejero's coup attempt, staged just years after Spain's transition to democracy following Franco's death, briefly held the entire parliament hostage at gunpoint before collapsing after King Juan Carlos I publicly denounced the plotters on television, a decisive moment that helped secure Spanish democracy.

Astronomers observe Supernova 1987A in a nearby galaxy, the closest and most studied supernova visible from Earth in nearly four centuries.

Supernova 1987A, the explosive death of a massive star roughly 168,000 light-years away, was the closest and brightest supernova observed since the invention of the telescope, giving astronomers an unprecedented opportunity to study stellar death and the origins of heavy elements in real time.

Germany holds a snap federal election following the collapse of the governing coalition the previous year.

The snap election followed the collapse of Germany's three-party coalition government the previous year over budget disagreements, reflecting a period of political fragmentation and economic uncertainty in Europe's largest economy.